If you model NSWGR diesel era and use DCC, there is a fair chance you may have a number of locos with 5 digit running numbers.
I have a few: 44222, 44100 and 48136.
Given that DCC systems (well, NCE anyway) only allow for a maximum of 4 digits in the address so the question arises, would you number the above locos as 4422 or 4222; 4410 or 4100; 4813 or 8136?
I have elected to drop off the first digit, so have numbered according to the 2nd option in each of the above examples. My decision was fairly easy as there is no such loco as 4222 (but there is a 4422); there is no such loco as 4100 (but there is a 4410) and as I model an era prior to the introduction of the 81 class, I don't have to worry about there ever being an "8136" on my layout.
The same situation arises for the 421 class and 422 class. If/when I get either of these classes of loco, they too will have their first digit dropped off and will be "21**" and "22**" as appropriate.
The reason I ask is that I had the model of 44100 converted to sound by Marcus Ammann and he asked me what running number I wanted him to program it as. He expressed surprise when I said 4100 as he would have done it as 4410.....but my argument was that one day I might actually get a model of 4410 and then I'd be stuffed. Hence my decision.
Sorry to waste more bandwidth about a useless topic, but I'm bored...waiting for 6 Tsunami sound decoders to arrive from USA so I can do more conversions.