Oops, I've got just over 12,000 on my tree - so I'm in the "one star, and if I could give you zero, I would" category.
I've been researching since the 1980's and was lucky enough to be given a tree for my maternal grandmother's line which had been very well researched by two distant cousins in the sixties and seventies. I checked it and couldn't find any errors. I could only add very small bits to it when more records came on line. That branch came from a small area in Yorkshire and the name was not common which made it easier, but nevertheless they must have spent weeks if not months in record offices.