Proper Thickness of Frictions

Since I’ve never taken apart an automatic before, I have no idea if those discs look like new or 1/2 worn out.
There was what I would consider a lot of material in the fluid. So if those look good, where might it have come from?
If they look 1/2 used up, then it would make sense to replace them, though I would still need to figure out why.
Watching the videos, I do see checks for proper engagement etc., though I don’t see anything about checking a converter.
I do plan on a better converter though.