Just to give some further insight, as a lot of the specific numbers were determined by me, and Criss and I just focused on the general layout for the naming convention.
jstenholt you're completely right in that aviation, such as Boeing does it differently than we did. The original inspiration for our system was in fact boeing, but in how it turned out the system become more like the numbering system for more industrial machinery, like heavy equipment or semi-trucks/lorries.
So to break down the model numbers even further we use a three-digit system for the model numbers. The first digit is the main class size, so because our first TG ships are all "small class" or Class 1 the first digit is one. The second digit is the sub-class size, meaning that it tells you the size of the ship within class one. So a model number that is "10X" is considerably smaller than a ship that is "19X". The third digit, which Criss briefly mentioned in his latest post correlates to something with their systems, could be engine number, number of cargo areas, weapon systems, etc. So the third digit is the most random, and not entirely useful.
The overall goal was to have players able to figure out what sort of ships they might be coming up to from a great distance, even just through the nav menu. If you're planning to raid a TG convoy, and see a lot of Bahtra 190's it's not as good of an idea to continue with the raid than if it was a few 105's.
I hope this can shed some more light on it as it's sort of a mashup of inspirations from multiple real-world sources while also trying to add in our own logic.