I've had the same issue with my Murdock ancestors. At times they are called Mirdock, Murdick. Marduck, etc. And first names are misspelled, etc. And at such times I feel life is easy, but when the Census taker gives that Murdock a different birthplace than the one of which I was aware, and all of the other Census records each do their own thing, Gosh, I want to go back in time and help them.
Census Law changed (laws pertaining to how one conducts the Census) many times over the last couple of centuries, so the person may--at times be talking to a kid who has no clue, or to a servant/daily worker on a farm (who does not really know but wishes to be helpful).
There is an article about this issue on the National Archives site.