I can confim this somewhat with personal anecdote. My family is one of the original 38 that settled New Mexico in 1598, and we know several other old colonial families. I know of at least one family that recently discovered their Jewish origins. This particular family was remodeling their 250-year old adobe home and found a mezuzah hidden in the wall next to the front door. They were shocked, being a very devout Catholic family. I spoke to the patriarch of the family about it, and he did mention playing with something like a dreidel as a child as well as an avoidance of pork. They were all very embarrassed about the whole thing.