Was there much overlap between the 6502 version and the 8088 version, or did it need to be completely rewritten?
I could see them having a higher level design, which could in theory actually be C code, which just needed to be rendered, er, compiled down to the specific instruction sets. I'm assuming all this assembly was written as assembly, but there could still be a higher-level design, rendered as flowcharts or whatever that was translated for each architecture.
It's a fascinating part of computer history. I miss those days, even though I never actually had my own computer until after I graduated from college.