Also the Touch is N905, N905 B, N905 C, yet the N905 C takes different FW, but the 6.8″ Aura H2Os are N250, N867, N873.
https://pgaskin.net/KoboStuff/kobofirmware.html
I can't see any logic to the numbering.
An N428 could be replacing any model. Which currently sold ones don't have USB-C? That's more likely than a new Libra 2.