Ciao!
Bridges were engraved with cutter and mask. The tip of the drill could be new or worn, then could happen bridges etched more clearly than others. The tip wear was more rapid in the processing of these bridges because they were carved after the nickel plating, which made the surface more hard. Over time I saw big differences between bridges 773x NOS. I noticed that some bridges were nickel after milling, some not (and were in contrast with the groove of the written brass color), always on NOS watches. For example, my Temporada has the bridge nickel after processing, an Autavia not.

Hope it can help...

Ciao and good luck with this auction!!!!

Pier