Thesecan hardly be called cinderellas (at least in the meaning I understand it),they are fakes to collect money from collectors, and they were not issued in the 1970s. They are modern artefacts of the same nature as "Mari-El Republic issue (Perhaps Mordovia)" (as mentioned by rod222
First, they imitate postage stamps of that period (the writing "USSR Post" and face values in kopecks, corresponding to the postage ratesin force then - 4 k(opecks) inland letter up to 20 gr, 6 k airmail inland letter, 10 k registered inland letter, 12 k surface international letter), and that was absolutely impossible at that time - the man who did it would have definitely ended in jail.
Second, cinderellas were issued in the USSR at that time - membership fee stamps (of the type I post here - modern Dynamo Sporting Society membership fee stamp from Belarus) or fund raising stamps issued by some All-Union (Federal) non-profit organisations, but they were never issued in sheetlets of multiples then, it started much later, in the last years of the USSR, and those were private initiative (which was punishable in the USSR in the 1970s).
As a kind of conclusion - these are modern fakes to fool foreign philatelist who are unaware of the Soviet and post-Soviet realities and can take them for real postage stampsor, at least official cinderellas, not just "money vacuum cleaners".
By the way, the above mentioned Mari-El Republic and Mordovia (I can add Buryatia, Tuva and a number of others have nothing to do with the breakof the USSR - they were and still are republics within the Russian Federation, and they are not stamp issuing authorities. So all those colourful piepce of paper with their names on them are productsof the same kind - fakes printed to take your money away, and are produced by the same people who "issue" stamps of K