Well we started with pickups so I'll post these here for posterity.
The very earliest 1985 factory made guitars came with 7 (treble) and 8 (bass) stamped PUs rather than T and Bs - probably only in the first fifty or so guitars off the line. These were in a 1985 Custom I used to own that was one of the very earliest serial numbered Customs made.
What I suspect happened is the stamping shop either didn't have a T and B stamps, or the drawings sent over were not clear and the T and B were misread as 7 and 8.
Edit - should anyone have a proper pre-factory Custom or pre-Standard (as in hand made by Paul himself) I'd love to know what pickups are fitted / how they're marked.