They are numbered so that the last two digits of the unit number follow consecutively the other two batches of London Midland 350s:
350/1s: 350101 - 130
350/2s: 350231 - 267
350/3s: 350368 - 377
Note that the 350/4 fleet is numbered 350401 - 410. Perhaps they'll become 350478 - 487 when transferred from TPE to LM in the future.
Or 411-420.
Except the whole point is to give the individual units in the LM fleet unique 'last two' digits. So that doesn't actually work...
Note that the 350/4 fleet is numbered 350401 - 410. Perhaps they'll become 350478 - 487 when transferred from TPE to LM in the future.
Even more so seeing as they still have and are keeping for the forseeable future 321411-417....
Unique last two numbers per class perhaps was the aim?