A Gen 1b P205 would have the size printed on the bottom. It may be rubbed off.
I do not have enough P320 pencils to know exactly how they would fall in the flow chart on the early side.
However, the mold marks of 7 & 8 do seem to indicate a Gen 1 pencil. Do the brass spring rest on the reservoir have a bevel or is it flat? I believe the beveled one is the earliest model.
For now, the 1971 P205A’s container tube doesn’t have a stopper for the eraser cap, so the cap sinks quite far into the body. A 1975 example is the same. I think @nimrodd will agree.
You could make a stop with the metal piece around an eraser. That is what was originally used. Just take it off the eraser, then expand it on the tip a little bit at a time until it is larger than the cap. Then compress it to put it in the cap, smooth side first until the ridged side is just inside the cap. Then slowly slide it over the eraser nail it stops.