That does not apply here. There's not an exact definition what a Scotsman is, except that he's from Scotland. Communism is actually a completely worked out ideology. It has never really been tried. In Russia for example, it was State Capitalism under the guise of Communism.
Communism has a lot of different varieties (you may be thinking of Marxism specifically), many of which have not been tried. While among Communists there might be some point in arguing over whether Leninism (and it's descendants, Stalinism and Maoism, etc.) are really forms of Communism or something else, in more general contexts it's probably better just to note the specific, rather extreme, departures from Marxism that they involve, and note that while they may have failed, those failures cannot be generalized to Communism more generally or, e.g., to Marxism specifically.
Forgive me but that's like batting aside misgivings about capitalism and saying, well that's neo-liberal capitalism or capitalism with eastern values, or government regulated capitalism, etc. When someone points out some deficiencies in capitalism. A form of not a true Scotsman argument.
