I cut the wires to one of them (c20) and replaced it with a more
modern cap.
The other two caps, c19 and c21, have only one wire coming off
them. My question is, did they intentionally solder the other
lead to the caps can for use as ground ? I'm looking at the
bottom of the can and cannot easily tell if this is true.

I just want to make sure before I wire replacement caps to ground.

Thanks......