Hi, no factory logs survive, according to Mr. Columbia. He gathered what information he could for a now defunct website.
I came along later, interested in production details of the G519 Military bikes, again johan Willaert's Liberator site was, and is a fantastic resource, but had little on dating the bikes. I started to collect known survivor details for the Westfield and Huffman G519's, and this eventually expanded to all prewar Westfields.Also, you gather other info as you go along. This bike will help more than many do, since it will help me resolve when MF series G519's were made, and MG series G519's. So, a good $20 spent, thanks (-:
And, yes, I think between 1 in 500, (0.2%) and 1 in 1000 (0.1%)survive, depending on the model, date etc. so there may be 12 1941 G serialed bikes out there.
I'm away from my notes at the moment, but I'll look later in the week to see if I have references of other bikes close to it, that could help with the tank/guard/rack question.
Best Regards,
Adrian