When you say a "bespoke system," do you mean a hardware set-up, or some kind of customized software that they use? If it's software, do you have any info about what it is or where it came from?

What was the encoding you used to make the font?

James

The bespoke software unfortunately is the only one of its kind in operation, and the makers disappeared into the ether soon after it was sold years ago. It runs on pc's, and perhaps I'm being naive here, but the encoding I used was 'default encoding'. The fonts also get converted into a software native binary file, but that's probably more of interest than of help.

The problem still has yet to be fixed and I'm now changing the encoding to 'windosws ANSI. I'm also weaving myself a long rope.

All you can do is give them a variety of options to try out, until you come across something that works. And give the optional fonts markedly different (silly, even) names and numbers, to avoid conflicts.
I've had various problems to do with naming and encoding, and it seems to me it's best just to find something that works, rather than figure out the whys and wherefores, or who's responsible.