[Dénes Bernád]

Thanks, Carl, for the informative post. It appears that these 5-digit codes were of similar concept to the German Wehrmacht's Feldpostnummern.

I found these codes recently, in a list discovered accidentally when looking through some wartime documents of the Rumanian airplane factory, I.A.R. Brasov. The mentioned list detailed the work done for the (by then) allied Soviets by the said factory in late 1944.