LU car numbers on NR

[norbitonflyer]

In Another Place (District Dave) speculation is rife about the recently-announced number range for the new Piccadilly Line stock.
Existing LU stock has 3 digit or 4 digit numbers, or 5 digit numbers in the 1xxxx, 2xxxx, 5xxxx, 6xxxx, and 9xxxx ranges
The new trains will apparently have car numbers in the range 38xxx to 48xxx (each articulated unit will have eleven bodies - I hesitate to call them cars as some will be wheel-less, supported by their neighbours) There seems to be no obvious reason for choosing such a range - why not start at 30xxx?
Although the numbering of S-stock (which runs on NR tracks in places) seems to have avoided the 212xx range simply to avoid duplication with the half dozen surviving Mark 1 BCKs, the Piccadilly Line does not share with NR and in any case the proposed range overlaps with a number of NR types, notably TfL's own Overground Class 378s, whose carriages are numbered in the 38xxx series.
Anyone able to shed light on this?

 

[bb21]

Not so much as shedding light but some thoughts on it.

Have you read John Hawkins' essay on LU carriage numbering history? I can't remember where I first downloaded it (possibly District Dave forum).

I wonder if the 3xxxx series was previously proposed for the S7 stock, and original plan all along (even back in 2007) for the 73 stock replacement (in 2012?) was that it would occupy the 4xxxx series, long before it was decided it would have 11 segments per train, so it explains eroding into either the 3xxxx or 5xxxx series (latter already partially occupied by the 95 stock). In any case 3xxxx did not happen and it may have just seemed convenient to utilise the higher end of that range. The clash with 378 car numbering may simply have been an oversight. That said, 51xxx-53xxx is unlikely to be reused before the 95 stock go so they could have equally used 49xxx and 50xxx instead of 38xxx and 39xxx.

Is the rumoured numbering confirmed, or merely conjectured or proposed? Even if it were announced I imagine it could still change if needed.