Thank you all for the reply, I think it was a typo due to below assumption.
1.if I understand correctly, the rifle was first assembled and tested to make sure working properly then stamped with SN.
2.if the parts got stamped first then assembled, the гд353 and ги353 should be 5000 apart from each other. so the chance of picking up wrong receiver cover is really low.
3.the rifle looks like non-refurb, or very light refurb. There's no refurb marking, original blue with some handling marks, all the SN are deep and clear.
4.if the rifle went through refurb process, how big the chance is that гд353 and ги353 wend through the process together and got receiver cover switched.
but on the other hand when stamp the parts, the person only need to put гд on his work station, other letter should be in the tool box.
everything is possible until I found гд353 cover or another ги353 cover.