Guys (it is me again )

From the few photos and articles I have describing events 1910-20 did any systematic numbering of aeroplanes in military service take place?

I doubt it, since from 1917 the aeroplanes received most probably kept their military serial once issued by France or Britain, so the question then is, what happened in 1919 when all the Hungarian booty came back? Was the original serial numbers kept by the Romanian authorities or what happened?

Finally when was the unhappy decision taken to issue aeroplanes with the simple system still going on at the outbreak of WW 2 and also kept probably post WW 2 for those types which continued in service to the mid 50's?

Cheers
Stig Jarlevik