I ran into a problem that looked like a single simple mistake. As I looked at immediate family members, it became an order of magnitude more complicated and you might say I can't see the forest for the trees at this point.
It started with a Holocaust survivor who emigrated from Germany to the United States during World War II. He had 2 marriages, with both children from the first wife, who died about a year before he left Germany. The abandoned gedcom says his second marriage was in US, but I documented that he traveled here with the second wife ... and an 8 year old child, who cannot be from his first marriage. The next thing I noticed was that the daughter from the first marriage was born 1 year before dear old dad!!!
I have a couple of sources, but not necessarily better than the original gedcom, however they do give me a starting point and are better than nothing. The gedcom info mostly agrees with them. In this case, I used the more extensive one to verify the family back as far as it goes and put notes about what is in the source on the relevant profile pages. This didn't help, other than to give me a clearer picture of the mess.
If you start from Moritz Gottschalk, you'll see where my troubles began. If you click on his wife Regina, you can see all my notes by surfing back through her family.
I'm now thinking that this Moritz did not marry Regina - she must have been married to a different Moritz - but at this point, I'm not even sure who I am any more.