[JdeBP]

One of the books was an entire annotated disassembly of the BASIC interpreter, if memory serves. I vaguely remember there being some sort of kerfuffle about that.

Another thing that one got: a printed circuit diagram of the machine.

As for today: One can get get an entire annotated disassembly for Elite, including the version that used the Second Processor: https://www.bbcelite.com