Oversimplifying but you're not wrong.
The undocumented mid year change in the ECU on roadsters mid 2014 marked a division of functionality. Any tunes built prior to that wont work on post update bikes and vice versa.
Each tune is built on the basis of a Triumph tune and modified from there to fit each bike by the owner, which is what I mean by base tune. For example, a 20355 map will not work in a post mid 2014 bike whos equivelant base tune is a 20776 basis. This is why on this page they are divided by VIN #:
Triumph_OEM_Tune_list. 3 & 4 Cyl. models
Touring models are different which, as I understand it for touring models (since I don't own one), you can flash anything to any bike as long as it was a touring base tune.