That's not really the only possible way. You could write an (arbitrarily slow & simple) interpreter in e.g. C to compile the compiler with itself, or translate

That's not really the only possible way. You could write an (arbitrarily slow & simple) interpreter in e.g. C to compile the compiler with itself, or translate to C, or use something like a p-code machine as an intermediate step (https://en.wikipedia.org/wiki/P-code_machine https://en.wikipedia.org/wiki/P-code_machine) with an assembler-written interpreter. The problem with using older versions is that in principle, you'd have to keep maintaining/porting them for newer systems/architectures.