The Russian made Big Muff pots also lack date codes.
I've heard that to properly date your vintage guitar, aside from serial number, is to remove the black plate and check the pot (potentiometer) codes which are generally 6-7 digits.
Now that being said, who's to say those posts are originals?
When dating a vintage guitar, you can't go by just one factor- you have to take all available information about that guitar into consideration and then make a judgment.
Pot codes are an important factor, but not the only one.
Couldn't they be replaced or changed along the way? So is the idea that all 4 pots should have the same date, preferably the date your guitar was manufactured (according to the serial number)?