The ref. 3970 series has been gaining popularity in recent years, with the first model with a snapback structure matching or even surpassing the market value of the ref. 2499 4th series from a while back. Among these, the ref. 3971 with a see-through back...
it can go straight to the museum as a vintage one - magnificent! I wish I could handle both side by side to better grasp the finer differences you mention. thanks!
Without the screw-down case back which was later featured and with the hallmarks on the back of the lugs and not on their side, it looks perfect. Best, Emmanuel