The BDY number on the tag was the order confirmation #, had nothing to do with production scheduling. I have paperwork for a dealer that had approximately 100 69s. Cars ordered and confirmed at the same time [sequential #s] were not only not built in order, they could be built over a period of several days. Confirmation #s can be thousands apart.
The actual production sequence # was on the body and chassis broadcast copies [Norwood workers called them 'sequence sheets']. Also, probably written on the body and frame someplace. I have a BBC with a notation stating three cars were not going to be built in sequence order.