@necro Ok, so seems 4.21 may be the prerequisite for G9 Dev Tools or its respective scripts to function properly - or at all. I've considered installing most recent and updated on a separate older machine for similar purposes, as well as the thought of running parallel on primary machine with separate, renamed folder technique outlined here at Zone. Latter has worked well for running a slightly more recent DS ver for the same things you use it for (volumetrics and other tools), (though apparently it's still not recent enough for G9 Dev Tools/scripts to work); but always leery about installing and running another version in parallel and screwing things up with runtime references or other.
Going to have to backup and get brave eventually I suppose.