The only thing we know for sure is that mine (gold moon) is early in the production and my friend's is later. I guess they made parts from time to time and changed a bit over time. There was a prior discussion about how they changed one of the bridges at one point as well.
Eight of us gathered to celebrate was our friends' 60th. One attendee and I wore the same watch -- 5004p. Mine is more opaline with a gold moon, the other more silvery and with silver moon. Menu and wines continued with dishes of duck confit, then beef, and cheeses from the region.
But I imagine it is a bit fragile with so many moving parts. It is not that old, but a bit, and feels somehow like an older design to me. I would not wear it exposed in rain or cooking. I have washed my hands wearing it will no ill effects so far.