Latvia 1992 Post Office Generated Cover

I collect Latvia pre-WW2. Back in 1992 I received this cover on some postcards that I had bought. The center stamp is Latvia Sc. 317 apparently on a Post Office printed cover but the left hand 'stamp' is imperf and unless sheets were printed to make up the rate for overseas mail(which appears to be 500k) could well have been cut from another envelope and applied. I'm guessing that maybe the whole cover was available for purchase that way from the post office since it was cancelled and made it to the US. My question is, is there a catalog number for the printed 100k cover and also is there a number for the 300k added 'stamp'. Or is there a catalog number for the whole combination? Any help you folks could provide would be much appreciated.

Maybe someone has the information. Otherwise there is :
Specialiizetais Latvijas Pastmarku un Pasta Sutijumu Katalogs = Specialized Catalogue of Postage Stamps and Postal Stationery of Latvia, 1990-2000 (Latvian) Paperback – 2001
by Egils Plume (Author)
It dépends on how important it is for you.Is it just for 1 cover or are you specialized?
Amazon lists one.I Don't know if its still valid…

https://www.amazon.com/Specialiizet...02011&sr=8-5

Your 100k stamped postal envelope has been uprated with the additional stamps. The 300k "stamp" is probably a cut out from another postal envelope and glued on. This is against regulations in some countries like the U.S., but tolerated in others. There would not be a catalog number for the combination of the cover plus stamps, but a specialized catalog would have information on the postal stationery item itself like in the catalog listed above.

Battlestamps my first thought was that it was a cutout too but it looks so neatly done that I was wondering if maybe the post office had done that as a way to make up the 500k rate.

Your stamped envelope is listed in the specialized catalogue (described by perf12) as #A16,and the cut-out is from #A17. Both envelopes are listed too in Michel ganzsachen (stationery) katalog.
Date of issue is 1992,July 18

Thanks for all the information. It helps a lot.