Hey, I'll have to check that one out too. They should have realized we, the fans, pay attention to detail and would notice this.
I found one with one of the Rich Little episodes. Near the end, Chico is tremendous as he does imitations. Rich Little says, "You're a fine Puerto Rican kid." Chico's character was Mexican. I think I even saw a tiny reaction and realization of the mistake, by Freddie when Rich Little said it.
