Yes, Frybabe I think that is how these stories came to be as we read them today - for hundreds of years various aspects were either blown up or changed to suite the experience of the audience and the skill of the storyteller. This aspect is so apparent in the many Ballads about the same character or theme - I have the Child's collection which was done in the later years of the nineteenth century that does include a few about Arthur and his knights but more about Robin Hood and then a few of the Chaucer stories are about the knights we are reading about - I think having a list of the names that one knight is called in different stories and languages would help me.
I'm thinking that Owain had some issue with his lady-wife --- there is a ballad about him and a lady who he meets after dark and is beautiful - he beds her admiring her beauty but when morning arrives with the light of day she is an ugly old hag and Owain has to decide if he want her beauty at night when no one will know he must accept her appearance in the day knowing everyone will see and assume he has married an old ugly hag.
In another version of this story a mother dies, and daughter Isabel's father marries a vile woman who abuses and enchants her till Owyne (Owain) shall rescue her. Owyne comes and sees a hideous beast. Despite her appearance, despite threats, he kisses her three times and restores her.
In another version of this same story Arthur, after Christmas, had been encountered at Tarn Wadling, in the forest of Inglewood, by a bold baron armed with a club, who offered him the choice of fighting, or ransoming himself by coming back on New Year's day and bringing word what women most desire. Arthur puts this question in all quarters, and having collected many answers, in which, possibly, he had little confidence, he rides to keep his day.
On the way he meets a frightfully ugly woman; she intimates that she could help him. Arthur promises her Gawain in marriage, if she will, and she imparts to him the right answer. Arthur finds the baron waiting for him at the tarn, and presents first the answers which he had collected and written down. These are contemptuously rejected.
Arthur then says that he had met a lady on a moor, who had told him that a woman would have her will. The baron says that the misshapen lady on the moor was his sister, and he will burn her if he can get hold of her. Upon Arthur's return he tells his knights that he has a wife for one of them, and they ride with the king to see her, or perhaps for her to make her choice.
When they see the bride, they decline the match in vehement terms, all but Gawain, who is somehow led to waive "a little foul sight and misliking." She is bedded in all her repulsiveness, and turns to a beautiful young woman. To try Gawain's compliance further, she asks him whether he will have her in this likeness by night only or only by day.
Putting aside his own preference, Gawain leaves the choice to her, and this is all that is needed to keep her perpetually beautiful. For a stepmother had witched her to go on the wild moor in that fiendly shape until she should meet some knight who would let her have all her will. Her brother, under a like spell, was to challenge men either to fight with him at odds or to answer his hard question.
And then in another of many versions of the same Ballad (Child traveled all over Britain, Scotland and Ireland collecting the Ballads - he included no music only the words sung to him with any description offered by either the singer or those in the house or village where he hears the Ballad) and some give this version another name as The Weddynge of Sr Gawen and Dame Ragnell
This versions has Arthur, while hunting in Ingleswood, stalked and finally shot a great hart, which fell in a fern-brake. While the king, alone and far from his men, was engaged in making the assay, there appeared a groom, bearing the quaint name of Gromer Somer Joure, who grimly told him that he meant now to requite him for having taken away his lands. Arthur represented that it would be a shame to knighthood for an armed man to kill a man in green, and offered him any satisfaction. The only terms Gromer would grant were that Arthur should come back alone to that place that day twelvemonth, and then tell him what women love best; not bringing the right answer, he was to lose his head. The king gave his oath, and they parted.
The knights, summoned by the king's bugle, found him in heavy cheer, and the reason he would at first tell no man, but after a while took Gawain into confidence. Gawain advised that they two should ride into strange country in different directions, put the question to every man and woman they met, and write the answers in a book. This they did, and each made a large collection.
Gawain thought they could not fail, but the king was anxious, and considered that it would be prudent to spend the only month that was left in prosecuting the inquiry in the region of Ingleswood. Gawain agreed that it was good to be speering, and bade the king doubt not that some of his saws should help at need.
Arthur rode to Ingleswood, and met a lady, riding on a richly-caparisoned palfrey, but herself of a hideousness which beggars words; nevertheless the items are not spared. She came up to Arthur and told him that she knew his counsel; none of his answers would help. If he would grant her one thing, she would warrant his life; otherwise, he must lose his head. This one thing was that she should be Gawain's wife. The king said this lay with Gawain; he would do what he could, but it were a pity to make Gawain wed so foul a lady. " No matter," she rejoined, " though I be foul: choice for a mate hath an owl. When thou comest to thine answer, I shall meet thee; else art thou lost."
The king returned to Carlisle with a heart no lighter, and the first man he saw was Gawain, who asked how be had sped. Never so ill: he had met a lady who had offered to save his life, but she was the foulest he had ever seen, and the condition was that Gawain should be her husband. "Is that all?" said Gawain. "I will wed her once and again, though she were the devil; else were I no friend." Well might the king exclaim, "Of all knights thou bearest the flower!"
After five or six days more the time came for the answer. The king had hardly ridden a mile into the forest when he met the lady, by name Dame Ragnell. He told her Gawain should wed her, and demanded her answer. "Some say this and some say that, but above all things women desire to have the sovereignty; tell this to the knight; he will curse her that told thee, for his labor is lost." Arthur, thus equipped, rode on as fast as he could go, through mire and fen. Gromer was waiting, and sternly demanded the answer. Arthur offered his two books, for Dame Ragnell had told him to save himself by any of those answers if he could. "Nay, nay, king," said Gromer, "thou art but a dead man." "Abide, Sir Gromer, I have an answer shall make all sure. Women desire sovereignty." "She that told thee that was my sister, Dame Ragnell; I pray I may see her burn on a fire." And so they parted.
Dame Ragnell was waiting for Arthur, too, and would hear of nothing but immediate fulfillment of her bargain. She followed the king to his court, and required him to produce Gawain instantly, who came and plighted his troth. The queen begged her to be married privately, and early in the morning. Dame Ragnell would consent to no such arrangement. She would not go to church till high-mass time, and she would dine in the open hall. At her wedding she was dressed more splendidly than the queen, and she sat at the head of the table at the dinner afterwards. There her appetite was all but as horrible as her person: she ate three capons, three curlews, and great bake meats, all that was set before her, less and more.
She chided Gawain for his 'offishness', and begged him to kiss her, at least. "I will do more," said Gawain, and, turning, beheld the fairest creature he ever saw. But the transformed lady told him that her beauty would not hold: he must choose whether she should be fair by night and foul by day, or fair by day and foul by night. Gawain said the choice was hard, and left all to her. "Gramercy," said the lady, "thou shalt have me fair both day and night." Then she told him that her step-dame had turned her into that 'monstrons' shape by necromancy, not to recover her own till the best knight in England had wedded her and given her sovereignty in all points.
In yet another version the hoodie, a species of crow, having married the youngest of a farmer's three daughters, says to her, "Whether wouldst thou rather that I should be a hoodie by day and a man at night, or be a hoodie at night and a man by day?" The woman maintains her proper sovereignty, and does not leave the decision to him: "'I would rather that thou wert a man by day and a hoodie at night,' says she. After this he was a splendid fellow by day, and a hoodie at night." Then there is a German version where the choice is a bear by day or by night...
And so with all of that I am comfortable that these stories were altered during various times and in various locations and even more, since they were written several hundred years after they were supposed to take place I am sure the morality and thinking of the writers enter these stories. Probably explains why these Welsh versions differ from the French version which differs again from the versions we have of Robert de Baron
