Standard human sleep staging criteria dictate that non-rapid eye movement (NREM) sleep begins with stage 1 (N1), making this a matter of basic sleep architecture classification that requires no external citation.
The claim states a definitional and observational fact about standard human sleep architecture: sleep onset into NREM is conventionally scored starting with N1 (stage 1). Because this is standard common knowledge regarding sleep staging rules, no citation is necessary and the balance verdict is COMMON_KNOWLEDGE.