Question for ya, I'm not all up to snuff on Ruskies.. were there many refurbs with no black paint? I'm assuming there were different refurb arsenals and maybe some didn't apply that?
There were definitely different levels of refurb and yes the refurb shops all did things a slight bit differently depending on the condition of the carbine needing work and their standard procedures. With really light refurbs, sometimes the original stock was simply sanded and refinished (but not reserialized) and the hard parts all left as original. People see those carbines and start tossing out "unfired", "unrefurbished", and "unissued"....except there's obvious shellac/lacquer fill in the stock S/N or a small refurb stamp somewhere.
The other light refurbs where the stock is XXX'd, a part is scrubbed and restamped, parts reblued, etc. is a much easier 'refurb' for most collectors to identify and ding in price, though if they are mostly left intact they can still get unwitting collectors to pay high $$ (think of the Ex-DDR craze back in 2010 timeframe). Of course, the heavy refurbs with BBQ black paint are the easiest to ID as you can see them from a mile away and most collectors know what they are.
At the very bottom end would be a bubba'd carbine that loses the most value (or at least it should, sometimes a bubba'd carbine will actually increase the value if the carbine was in notably bad shape prior to the work being done). I guess the bubba'd guns that simply have a stock change would be in a different category than say, a gun chopped to 16" with a muzzle brake welded in place too.