I never realised Caitlin was irish and had a different original pronunciation - learn something new everyday hey! Interesting how that name with it's changed pronunciation has become so common, whereas other irish names have retained their original pronunciation. Maybe because Caitlin does look so "normal" and easy to pronounce it never occurred to people it wasn't meant to be that way, whereas some other names, such as Siobhan, never look quite "right" e.g. See-Obb-Harn doesn't sound like a "normal" name so even pronounced phonetically it's unlikely to be mutated so frequently.
Same here I always thought Caitlyn was pronounced "Kate-lynn".
Well, as Corvid said upthread, since about the 80s, Kate-Lynn seems to have taken over, and Kathleen seems to be out of favour in any spelling. Oddly, this was being discussed recently in the UK press with the impending centenary of the birth of Dylan Thomas - it was being pointed out that commentators were referring to his wife as Kate-Lynn whereas she pronounced it Kathleen.
It was also being mentioned that Thomas himself deliberately shifted the pronunciation of his name towards the anglicised Dillon and away from the Welsh Dullan that he had used as a child.
I imagine that my irritation at Kate-Lynn - I didn't say it was reasonable, just that it annoys me - was shared previously by some people over the shifts of Evelyn, Sidney, Valentine etc from male to female.
When the Younger Chick was born, my parents were concerned that we had given him the name of a cartoon character of their youth, and weren't we worried that he would be teased about it? We had to point out that nobody under 40 had ever heard of that cartoon. Times change (she said with stunning lack of originality.)
If you want a name well provided with traps for the unwary, try Bridget. Brid is a variant in its own right, not just a contraction. It may be pronounced as in bridge, or bride, or breed, or breege, or breesh. Bride, also a name in its own right, may be spelled Bride or Brid, and pronounced with or without the final e. Bridie may be a pet name for Bride or Brid or Bridget, or it may be how she says Bride. Bridget pronounced the way you would expect can be spelled Brigid, or Brighid...