I find errors almost on a daily basis in some county.  I notify the clerk's of the errors and am told they keep record because I was very concerned that someone might have done a search and not have found it the day before.  They ask me how I find all of these mistakes - I tell them I'm a professional researcher - that is what I do for a living.  Now if they did the search properly in most instances they would have found the document - the cross-referencing I was talking about - however - if it was say an AJ - it is not attached to a particular property so it is not cross-indexed by property so if there was a typo it could have been missed.  But then again - I run my names all different ways to double check - it is part of why I am a professional and not a person sitting in front of a computer saying I can do the entire United States having no clue as to what each county's little quirks or mistakes in indexing are.