I have never seen a 38A with a folding bayonet. That's not to say they didn't exist just clarifying the limit of my knowledge. Both the 1938 Moschetto and the M1918/30 which are more or less contemporary models to the 38A used underfolders which required a very similar groove in the stock forend to protect the bayonet tip so it seems entirely probable that this was done on a 38A with an ubderfolder

 

Model 38A produced in 1938 for the PAI (Polizia Africa Italiana or Italian Africa Police) and for the Italian Police had the folding bayonet. Only about 5000 were produced and the iron bayonet is very rare and priced. From 1939 they were superseded.
These models were produced as 38A/44 again on years '50 for the Egypian Army and the bronze bayonet is some time faked as pre war.
Can you send us a picture of the entire gun?

 

Kanister

Here you go ...

Let me know what you think!

 

That is beautiful. I've never before seen a 38A which didn't have Beretta's manufacturer information marked atop the receiver. Its absence is fairly common on 38/42 and 38/44 models but yours is the first 38A I've seen without (admittedly a VERY small sample size, only a handful of guns)

 

A regular model 38A made on the first years of war, perhaps they used a stock found in some warehouse.
Only strange thing is the lack of marks atop the receiver.