[Arran]

You mentioned the production runs but often Philco would have various code numbers denoting design changes such as code 121, code 122, etc, the production runs would be in some sort of chronological order I think but the code numbers are not. The code numbers are not improvements as such so much as circuit designs that they follow according to what parts they had available, near as I can tell. I don't know when Philco started using the coded versions or if they were in use while the 80 was in production (I think they were) but make sure that the modifications they list match with the code number before making them.
Regards
Arran