It's a matter of not accepting the changes that the record shows, when you add it. You can accept the change (that on the left side when adding a record) as a "difference" like the software is indicating or you can uncheck and keep it (the right side) how you have it typed and just let the document/source get attached. No messy timelines this way.
People are not looking at what the record on the left is saying is different and then or also not realizing they don't have to use that, but can just keep the right side the way they already had it.
Thus people are getting all kinds of name messes & screwed up dates/places in their trees.
I very seldom accept the change on the left side when attaching a record/source. I use the right side that I already had input, OR, if I know the part on the left is correct, I'll change my info on the right (and 'still not' accept that on the left side because it will insert in the timeline twice) or if mine is blank, THEN I will accept the left side and let it be inserted, as a main part of the fact. Not an alternate.
I accept very few 'alternate' additions. If I have any, it's because I intentionally let them be added. Or, I've added the alternate myself, on purpose. And I do have quite a few. But they are what I want or need. Not garbage clutter.
Which is pretty much what I think you, BrklynBridge, was saying. But maybe a slightly different wording helps. Say or phrase the same thing in enough different ways, eventually everyone can get it. We all have different things that we get in some ways, but not in others.