Fascinating thread.
I know nought about drives, but I have dealt with master, slaves and node addresses on RS-485 and RS-422 multi-drop setups in other contexts. Once I read the docs and got my head around the idea it was pretty straightforward, and in line with what Ken is describing for multi-drive mode operation.
There is something to be said for having all comm parameters, including node addresses, set via DIP switches: it may be cheaper to build, and easier to set things up initially via a screen because grokking the correlation between decimal addresses and their equivalent binary form in DIP switches is not everyone's cup of tea, but the long-term advantage of the simplicity of maintenance staff knowing that to replace a device they need to duplicate the DIP switch positions without understanding what each switch means seems far more valuable. From what I am reading here, it appears that not having such a setup, along with inadequate (non-existent?) documentation, is why the system failed in the first place and was switched over to the pots, because that was what could be understood.
I look forward to the next chapter in the saga ...