That is where a lot of the confusion comes from. But i suppose in essence, that's what you have to figure out. the silent H in Irish is another thing but you have to remember what the irish version's of the name are and that' where a lot of the pronounciation.
I wouldn't rule out the "O'Carty" clan just because they are a small clan, and because of the mc's being dropped etc in America. I've lived in Ireland all my life, as has my family, and we are all without h's and a mc.
Fraid i've never been in America, so no that was not me.