I’m honestly still not sure what you mean by science didn’t exist at the time or what context you might be referring to

You aren’t supposed to build communism, we are supposed to build socialism, only when generations are reared in the social conditions of the socialist mode of production, and the international conditions allow, and the productive capacity allows, can the transition from socialism to communism take place.

Basically we are too far off from communism to build it directly and to predict the fine details of what it may look like, we need to build socialism first