B type helmet

I own a B type flying helmet with an owners rank surname and service number marked inside. I have attempted to research the owner to no avail untill coming across a supplement in the London Gazette listing his surname initials and service number plus incorrect rank. I have found another later listing in the Gazette full name old service number and a new number in brackets. All the other listings for air men on that page were the same. Does anyone know why service numbers were changed? Could it have anything to do with commissions?