https://www.gunbroker.com/item/989937787
Most likely real IMHO.
-This serial font is seen on the refurb imports.
-The finish is largely intact around the new serial stamp.
-Serial numbers with no prefix are also not uncommon on replacement stocks.
-I also think this particular cyrillic prefix "НБ" would be easy enough to fake
If i had to guess, this is a very late replacement stock.
I've begun to wonder if examples like this -- Late production refurb, with partial stock serial, and no crossbolt at the wrist-- might be an indication that the late final "refurbishment" was part of an aesthetic, commercial make-over and not intended for re-issue.
Who knows.
I totally missed the Listing title:
"Norinco Type 56 sks" stop1
Not unprecedented to have numbers only on the refurb stock for a Soviet SKS45. Here's the first one I found, off a prefix AB carbine from 1954.:
(https://i.ibb.co/2YP2SyF/AO1638-stock.jpg)
Interesting that the original stock was prefix "MT". Just for grins I did a search for MT prefixed stocks under my photos and turned up a bonanza of numeral only stock restamps (many more than I would have expected to see!):
(https://i.ibb.co/qR6JBqC/MT533-stock.jpg)
(https://i.ibb.co/9G52gfx/MT1088-stock.jpg)
(https://i.ibb.co/cNcvxdn/MT3785-stock.jpg)
(https://i.ibb.co/BL07LWC/MT5509-stock2.jpg)
(https://i.ibb.co/xfcMTB7/MT5571-stock.jpg)
None are as pristine as that 1955 cartouche on the OP carbine, but I would lean towards this being the norm during a certain refurbishment time period/facility.