Lyndel, you are awesome: Not only with your knowledge but also with your quick reply!

Following your lead I discovered that I own an older TSU9600 (not the backup I just bought on line) with the application 4.0.17 and the firmware 2.1.25.1 and a bootloader 1.2.8.
My recent addition lists as application 7.3.3 and an IR firmware 4.0.20 with a bootloader 1.2.8.

This information is confusing me, because I was under the impression that the info under application describes the firmware that requires PEP/96 v1.1.20. So what's the difference between application and firmware? And while we are at it - what is a bootloader that didn't change?

I also have a follow-up question:
Can I reload / return to an earlier version than currently installed? Namely from 7.3.3 to 4.0.17 if I should want to?