I think this panel wiring is pretty messed up but I want to confirm I'm looking at it correctly.
My house is from 1960 and has mostly the original ungrounded wiring (2-wire cloth NM) for branch circuits. The panel inside the house, where all of the branch circuits originate, is actually a subpanel. It's fed by a 100A breaker on the main/meter panel, located outside. The house subpanel is a retrofit circa 1985.
It looks to me like the 4-wire subpanel feed was wired with the ground going to the left bus, and the neutral on the right. I don't see any strap connecting the two busses, and no bonding screw on the neutral side. So the ground and neutral bars do seem to be isolated in this subpanel. But it looks different to photos of other panels I've seen, where the two busses on either side of the breakers are tied to neutral, with a separate ground bar off to the side.
In my case the branch circuit neutrals are wired to either side without any regard except for which was closer. Only one circuit has an EGC going back to the panel (a 240v circuit for the AC condenser) and that EGC is landed to the neutral side. I understand you might mix ground and neutral in a main panel where N and G are bonded, but not in a sub.
Mainly I want to see if more experienced people agree with my assessment of what's going on with the left and right busses.
EDIT: Adding a photo of the wiring diagram on the panel. On the diagram it looks like there is a strap that connects the two busses, but I cannot see it. If it exists it is behind the plastic frame which seems odd.
Also I do not see the neutral bonding screw in the location shown on the diagram.
Here's a shot of the text at the top of the panel diagram: