Le Morte D'Arthur
How we cite our quotes:
"Than woll I have hym in examynacion myself – for tyll that I know what is his ryght name and of what kynrede he is commyn, shall I never be myrry at my herte." (203.10-12)
Lyonet is understandably cautious about hitching her wagon to a man with a mysterious identity. She'd rather question Gareth on her own, than simply take the dwarf's word for it.
"A, dere modir," seyde Sir Gawain, "I knew hym nat." "Nothir I," seyde the Kynge, "That now me repentys, but, thanked be God, he is previd a worshypfull knyght as ony that is not lyvyng of his yerys – and I shall nevir be glad tyll that I may fynde hym." (210.39-44)
Because Launcelot has promised not to reveal it, Morgause must reveal Gareth's identity to the court. His mother would be the most logical source of this information, since she would know better than anyone whose child Gareth is, right? Right. So Gareth's identity is absolutely verified, beyond a shadow of a doubt, by his mother, just as Arthur's was.
"Sir," seyde Tramtryste, "now shall I tell you all the trouthe. My fadyrs name is Sir Melyodas, kyng of Lyonesse, and my modir hyght Elyzabeth, that was sister unto Kynge Marke of Cornwayle [...]And because I wolde nat be knowyn in this contrey I turned my name and let calle me Tramtryste. And for the trwage of Cornwayle I fought, for myne emys sake and for the ryght of Cornwayle ye had possessed many yerys." (242.14-20)
When Trystram hides his identity, it's to protect himself from the vengeance he knows the Queen of Cornwall will seek for her dead brother. When he reveals it, he "comes out" specifically as a Cornish knight, as if to say, hey, it was nothing personal. I'm Cornish, too.