It is really confusing when different descendants use different information on their family trees.
I do not use other folks trees ( or information on the tree) from Ancestry or Family Search as sources because of things you mention. If the trees have sources, I use the source. Otherwise, I use the information as hints and try to prove it.
If I cannot find a real solid source, I make an estimate (also guess) for dates and I mention in the bio how I computed the date.