Ah, the disc max. is 99, that must be what I vaguely remembered. So effectively 99x999 if I want track numbers to be valid. That's fine for what I'm after.
As for "in the digital media world this limit does not apply", that's very true. But software development means compromises are made, limits are put on structures mainly at the whim of the developer. Which is why I thought I'd find out, in this case, what those limits are.
Sorted.
David