>> Implementing some form of "distributed sequence" where each node uses
>> separate ranges is a reasonable solution to those conflicts that would
>> arise as a result of "internal interlinkages".
>
> All you do is make one db use even numbers and the other use odd by
> setting start and step values of the sequence.

How, in that scenario, does one introduce a fifth "master node"?

If you have one office that is an asynchronous node, that could easily be
extended to needing five offices.  Or 37 remote salescritters, each with a
database on their laptop...

It's not too difficult to solve the "distributed sequence" for the case of
two nodes, as even/odd does work out quite nicely.  Generalizing is not so
easy...