According to certain photographs during the Soviet invasion of Prague in 1968, seems like the second model of TSh-4M already existed in 1968 as well. For examples: - https://www.reddit.com/r/HistoryPorn/comments/98uaau/on_this_day_50_years_ago_1968_the_soviet_union/ (image 18) - https://www.theatlantic.com/photo/2018/08/photos-50-years-since-a-soviet-invasion-ended-the-prague-spring/567916/
Introduction year of the second version[]
Agree, it definitely existed.
Subsequent research through various photos and footage of Soviet Army of the Cold War era, I myself have also later found out that the second version (as the most widespread one) was actually introduced a few years before - back during the second half of 1960s (although it still remained much rarer when compared to the previous version up until the 1970s).
At first, and based on all the available info I had back then, I came to a conclusion and was pretty much assure that the second model was introduced yet in the early 1970s - being simultaneously adopted along with the-then newly introduced two-piece tankmen suit. However, it turned out that it actually already existed in the late 1960s and the suit was solely introduced in the early 1970s.
Anyway, it will be corrected (I am planning to generally refurbish and improve the article in any case). :)