Fed 1G Extra Serial

I was fixing this camera for someone else when I faced this small discovery.

A top plate serial number.
Can't remember this number on my Fed 1G, or I've maybe forgotten. Feds are full of suprises

Milo,
I am afraid to disappoint you, but it seems to be an inventory number of the top plate and it has not anything in common with the serial number

Regards, Alexander

Dear Alexander,

Well, thats not dissappointing anyway. Now I can think of a reason why they did such. Its the first time I found this.