I'd say the traits that are in the 100% or 99%
certainty category are* :
--Stamped matching font numbers are a sign of originality
--Matching stock with arsenal cartouche (except later Tulas), year and full serial number are original
--Refurbishment arsenal markings are a sign of refurbishment
--Black paint is a sign of refurbishment
90% ? *
--EP'd gas tube, gas piston, rear sight leaf and extractor are all likely original
Many other features or characteristics are probably in the uncertain, 50% category* :
This includes EP'd buttplates. It's probably just as valid, and unfortunately just as unsubstantiated, to say that an EP'd buttplate is a sign of refurbishment, or a sign of originality.
--A working hypothesis that the buttplates were EP'd in storage, to make them easily inventoried on horizontal racks seems plausible (but again, unverified)
--A working hypothesis that "Gen. Vodka of the east had his men EP their BP's to keep rifles parts identified" seems a stretch
(I know you were joking for effect Bob)
--A working hypothesis that they were EP'd at refurbishment seems plausible but unverified. Are the EP'd buttplates associated with certain refurbishment markings (i.e., inconsistent across the GRAU system)
--A working hypothesis that they were EP'd at Tula/Izhevsk originally, seems plausible but unverified. Why wasn't the practice consistent?
* Not exhaustive lists, just examples Caveat emptor: if you get more than one man discussing anything, the likeilhood of 100% agreement tends asymptotically toward zero the longer the discussion continues.