I can answer the question.
The Torx numbering system was derived based on 2 things, the diameter of the screw fastener to which the head was to be applied and the torque range for that diameter screw fastener. This then resulted in a universal difference in the point-to-point diameter of the Torx head and the screw fastener diameter.
Torx numbering is based on group ranges. 1-10, 20-30, 40-5, etc. The first digit (0,1,2,3 etc) defines the group and the required difference in Torx head P-P diameter vs. screw fastener diameter. The second number defines the Torx size within that group range.
Here is a quick table I put together to show how it works...
View attachment 1715049172
This is also why there aren't Torx bits in every size within a group. Since the threaded fastener diameters don't vary that much within a group range as the sizes get larger, there isn't a need for every possible size within that range.
So there you have it, the numbers do have a logic. :D