It is internet rumor that "only /26\ guns can be dated". Almost all Chinese type 56s have coded S/N prefixes. The patterns were readily apparent when the sample size got large enough.
This needs to be on the Chinese SKS site front and center... Unfortunately many people still believe this myth til this very day.
The dating system, or to be more accurate, the serial format, was first published circa.1955 by the 2nd Ministry of Machine Building (the department responsible for armament) but not fully adopted until 1960 or so. The switch was first observed on Type 53 Mosin carbines (M44 copy) made by Factory 296 in 1955, when the serial immediately jumped to 3 million despite the total contract was 100,400 newly produced T53 and 201,440 longer Mosins converted to T53/M44 standards, and the samp changed from 296 to 26, but no triangles yet.
The serial format had three noticeable features:
- No more "year" in the type designation. For example 五三年式 (53 Year Type) becomes 五三式 (53 Type).
- All state factories with 3 digit codes are shortened to 2 by removing the middle digit*. Factory 626 became 66, 296 became 26, etc.
- The first one or two digits of the serial denotes the nth year in production.
*this one didn't last long obviously, they soon ran out of the unique 2 digits so they removed this rule for all newly established factories
Tried to attach an image but no worky.
Source: Xiao, Wu, "The Cornerstone of the Chinese Military Industry: State Factory No.296",
Small Arms, Issue #6, 2021