Jacques, hat's what I love about these cameras - everytime you look at them you find something new.

I previously didn't pay much attention to shutter box material and holes in pressure plates, that's how it looks:
Film plate does have a hole in all my FED-S.
Also two normal FED c and d have the hole, FED e doesn't.
Shutter box:
FED-S c No.69929: Brass
FED-S d No.2570: Aluminium, "5" stamped on bottom if you look through lens mount
FED-S e No.174186: Aluminium, "33"
FED1 c: 60570 Brass
FED1 d: 129277 Aluminium
FED1 e: 174186 Aluminium
Can't check FED-S No.70883 as it is loaded with film, but it does have the hole.
Aidas says that Aluminium was used from #125.000 onwards, so maybe first and last digits are missing and it should read "125.70x"?
Regards,
Christian