For some reason never paid much attention until recently. The fonts of the 'year number' and 'serial number' on original non-refurb Izhevsk SKS stocks are quite different, especially the numbers '1' and '4'.
Does it indicate Izhevsk SKS stocks were not made in-house?
Don’t know that it indicates much beyond different stamps were used for the cartouche year vs the serial number. Fonts change, there are subtle differences in the numeral fonts at Tula from year to year as well.
There is a possibility that the final process before leaving the woodshop, was to stamp the crest and year. Then at final assembly the serial number would be stamped. This could account for different fonts. No proof of this, just a guess.