Thank you! I mistakenly assumed that this is order number because in this case it is the same for both sides. But it is rather exception than the rule - in most cases they are not the same. If it is a serial number, it has a very little value and probably even does not worth to be included in "other numbers".
While I typed it, I was getting doubts. I must have been told it, and it's true they are often close rather than the same on both sides. I'd like to find two copies of the same record to be absolutely sure.
I've found two copies of the same Fonotipia and they have different numbers. They must be serial copy numbers. I just wanted to be absolutely sure, I didn't want to create a new urban myth!
Gramophone did this also, but only as far as I know for Tamagno's original issues.
I've seen Fonotipias that the artist has signed in the wax, but I can't remember if they were French. In my search for a copy of the same record with different serial numbers I came a cross a number 11 online.
Some French artists actually signed Fonotipia labels in black ink in place of the blue rubber stamp. Hand signed discs usually bear one- or two-digit serial numbers.
The recently auctioned Amelia Pinto, L'Ebrea disc on Italian Fonotipia bears serial number 2, but the signature is stamped.