They were and are truly attempts at building communism. They were “true communism” in that sense. At the same time, they have yet to reach the stateless, classless, moneyless society stage where production and distribution is fully collectivized and oriented towards satisfying needs that communists call “communism” as a mode of production.

The “not true communism” argument more refers to those that incorrectly deny the USSR, PRC, Cuba, Vietnam, etc as validly socialist states working towards communism, not those that acknowledge them as genuine.