Received this a week or two ago (been waiting 4 weeks for Sigma to return my DSLR with lens sent for calibration ). From Aidas' wonderful classificator, the earliest Type B9 (with the top cover indentation) so far is 46988. This one is just a few hundred earlier, 46526
Hi Paul! These last Fed 1b are most interesting! In 5000 numbers or so, the curling on knobs changes, there is no more inside body screw, the top of the shutter release button becomes semi flat, then with concentric circles and the cam of the rangefinder becomes triangular. If I don't forget something!
After, it's the 1c: a line becoming almost straight... These 1b are my favourites.