The dates stamped on refrubished guns are often incorrect. Stocks and receiver covers were often replaced at refurbishment-- the serials were often struck or scrubbed and restamped to match the refurbished rifle but the dates were commonly left intact.

It is odd that your rifle would have the early trigger group -- since the dates suggest that the rifle was refurbished anywhere between 1954 and 1958-- but it is not unheard of. I have a 1950 Sovieticon Sneak that is a mix of parts from early to late (early trigger group with late magazine-- all matching except for a chinese reciver cover).

Best way to narrow that date of manufacture is the style of the forward gas port(90degree, 45degree, or Curved) and the number of tabs (1 or 2) on the take down lever on the rear site block.

Also the cyrillic prefix of the serial number may help to narrow the date of manufacture even more precisely.

Can you post some photos?