I try to understand how the RAF serial numbers were allocated. Normally I was thinking that the serials were given to the manufacturer as the contract was signed and were given in sequence. But that doesn't work with the French contracts transferred to the BPC in June 1940. What it is surprising is that for the Mohawks and early Bostons, the serials belongs to various range of numbers, AR, AX, BB, BJ , BK, BS, BT for the Mohawk, and AE, AW, AX, BB, BD, BJ, BK, BL, BT and BV and were given from August to at least November 1940. This oddity works for the contracts which were under delivery in June 1940, because for the Boston (Havoc) II, yet to be produced, the full order of 100 copies will receive a simple range of serial number (AH430-529).
If I can understand that the AM had to inventory what the RAF might expect to receive from contracts under delivery to the French in June 1940, that explanation is available only for the first days or first weeks after the transfer and no more available far as in October or November 1940 when the last Mohawks or Boston I were allocated their last serials (and built as the last Mohawk from the French contract was built in August 1940). Curtiss or Douglas were able to provide the information very quickly of how many aircraft had still to be produced. I must add, that except for the first 16 Bostons which were diverted at sea and arrived in UK in July 1940, all the Mohawks and the Bostons were delivered to the British in the USA. It seems but it needs confirmation, that actually the serials of those types were allocated when the aircraft had reached the UK.

So my question is simple: Why the serials of the Mohawk and the early Bostons are so fragmented?