The current limit is 250 instances of the same person.
Many of the issues can be resolved by looking for anything that doesn't seem right, usually what you look for is where the person was sealed to a person and the relationship has been disproved by other data, skipped generations where the person was sealed to a grandparent, and other types of merging errors in various databases.
The two biggest areas/time periods where this was most common are:
LDS pioneer era, particularly Nauvoo to after 1890s. Can be especially problematic where polygamous relationships were involved, while those are quite few relatively, the data in the system regarding there can be voluminous.
American (US) Colonial era. Can involve many from the LDS pioneer area, where they have gotten lines back into particularly New England. The further south you go in the colonial areas, the less you run into this although there is still some.
I've seen a few issues with England and even the areas covered by Germany and the Austro-Hungarian Empire, but those are usually scattered and are not usually too large.
The best way to pare away at the data is to look for obvious major errors. However, if one date is right but one is obviously a typo, like I've seen where a person born in 1660 was shown as being born in 1600, or one that I saw that had the person dying in 1547 when it should have read 1847, those don't have to be pared away if the rest of the info is rightm adding an opinion if no correct date exists is usually enough and the error suggests the correct date. Tree pruning will be 'de rigeur' for many who have pioneer ancetry or Colonial US ancestry for some time to come.
.... hmmm... need to check many to know for sure!
