As far as i know deliberate saves go into the "normal" files and auto saves go into the backup files on the project folder.
I can understand some confusion here, Especially because i get confused easily but the most likely couse of your confusion is that you forgot to save your project yourself.
but as others have said before me (bobc) this behaviour is easy to check with a little test project.
I seem to be misinterpreded here.
I don't really mind, I get that a lot from people.
It is just because my brain is wired a bit differently from "average".
Autosave can be sightly usefull sometimes but I just don't rely on it.
Consider this scenario: You've got an almost finished PCB but you get stuck because there is no room for the last 5 traces ....
throw way half the traces, move some components, redraw.
A very easy way to keep track of your backups is to give them dates in ISO8601 format
It is the best date format, worldwide standard. I like good standards, and wherever there is one I prefer them over local customs, especially if they are old customs. It's called progress.
The big advantage here is that files are then always listed in chronological order:
You'll get the idea.
And some more about AutoSave:
A few years ago I worked a bit with Blender.
Wonderful piece of software, but with quite a steep learning curve.
I abandoned it quite fast though because it was not the right software for me.
(I was more interested in mechanical CAD design, Blender is not good at that).
One thing I do remember (a bit) though is it's wonderfull "auto save" function.
It is also one of the weird features which take some time to get used to.
There is no way to save a project / file in Blender.
If you're finished for the day you just close Blender.
No save dialog, no questions, it just quits, there is nothing to save.
Even if you just pull the plug from jour PC halfway an edit you lose (almost) nothing, (If you have a decent jounalling file system).
The reason behind all this is that projects in blender tend to be so big that they wouldn't fit in memory anyway and the SW developers at blender have adopted to that completely by maintaning the "master" database with "everything" on disk and loading small parts temporary from the database when they are needed.
As far as I know it also comes with "infinite" undo, well, not infinite, it only goes back unto the first object drawn in blender I believe it's database has git-like features but it's all completely handled in the background and transparent to the user.
Very well thought out & advanced file handling.
If you don't like my rambling's then just ignore me, don't start complaining.