The IDs do seem to be changing. I can't work out how to post an image from my PC into this forum but with two X-Touch Minis plugged in, AAOs shows MIDI IN with IDs 1 to 3 and MIDI OUT with IDs 4 to 7. With the three controllers plugged in, AAOs shows MIDI IN with IDs 1 to 5 and MIDI OUT with IDs 6 to 11. The MIDI OUT assignments are very much changed (affecting LED commands for example). One of the X-TOUCH MINIs moves from ID 7 to ID 11.
In testing the above, I looked at a plane that I set up yesterday to use the X-Touch. In the "Change Button Assignment" screen, the Device showed as "X-TOUCH MINI # [1]" and the Assigned button/key as "CHN: 11 EVT: 2003 TURN_LEFT". After the testing, the Device had changed to "SMC-MIXER-Bt # [2]" with the assigned button/key unchanged.
If this had been set up with the SMC device, the assigned button/key would be different - for example "CHN: 1 EVT: 3031 TURN_LEFT".