Interesting Russian SKS 1952?

I found it on gunbroker, it ended up selling for $790. It has been refurbished but has all numbers matching. The receiver cover is dated 1952 but it is a "letter gun" with a tula star on the left of the receiver. I thought those were made in 1955/56? I have a star receiver SKS and the receiver cover is blank where only a refurbished stamp is [/].Is it possible the Tula star was added or that maybe the arsenal had dated "blank" receiver covers and just added the serial number of the gun being refurbished? Or maybe this disproves the theory that these were only made in 55/56.