Wouldnt it be a simple matter that at the end of the war, the B1 FE’s were new and un-used and available in storage, having not been used for the Far East, and that B1 production would had stopped by then to give way to the Lincoln?,

Ah – I think that was the bit I was missing. I’d assumed that FE conversions were applied to in-service aircraft. Had not realised that it was applied to new aircraft straight from production. Makes sense now. Thanks.