From N Gauge wiki
Pete33: The big question with stocklists is how do we want them ordered. By stock number? By locomotive running number? Or by company? It's important to work this out before the lists become to big.
Tank: How about year of release?
Pete33: To be honest, that would have been the hardest way of doing it (at least as far as I can see). I have absolutely no release data available, so until this morning (22 June 2013) I had them ordered by wheel arrangement, starting with the big boys and working down through the ranks to 0-6-0s and the like. Now I've added a sort facility to each table, so readers can make up their own minds about it. The default is still wheel arrangement, and that's how data should continue to be entered into the tables in order to maintain that default.