When initially established Gosplan didn't have the powers that it was later obtain in the command economy. It was a relatively small organisation which was mostly intended to advise on economic matters. They produced broad plans but these were more intended targets, rather than something that Gosplan was in charge of coordinating industry towards achieving. As you've probably figured out under NEP with there being a greater tolerance for markets/private ownership there would have been little for Gosplan, or the party-state in general, to work with in terms of commanding units of the economy - only those larger enterprises that were state owned.

Trotsky was one of the early advocates for Gosplan to have a leading role in actually setting detailed plans, and having those plans actually be accountable documents. This would essentially be implemented (with mixed success) in the first Five Year Plan, under Stalin.

The first volume of Stephen Kotkin's Stalin biography - the Paradoxes of Power - covers a lot of those early debates about the future of the economy/planning, and the seeming absurdity of having Gosplan, such a small state entity, run the entire economy.