That series of saws started with the Partner P7700 in about 1983/84.
here is more on it; "Missing link"
I don't think Pioneer had anything to do with the design.
As far as I know, the "family" consisted of;
-P7700, 2077, 475 and 2083 II with 77 cc engines
-2083 and 515 with 82.4 cc engines
-415(?)/425 with 65 cc engine.
All saws were made in Sweden.
Poulan Pro 445 is unknown to me, and not listed on CSCC.
The 65 cc engine is a bit small for the size/weight of these saws, so I would consider getting one with bigger engine, and use the 415 as the parts saw....