Final answer:
The correct resource frequently referred to in the CPT procedure nosology help messages for the correct assignment of E/M levels is the CPT Codebook.
Step-by-step explanation:
The correct resource frequently referred to in the CPT procedure nosology help messages for the correct assignment of E/M levels is the CPT Codebook. The CPT (Current Procedural Terminology) codebook is a standardized manual that provides detailed information about medical procedures, services, and billing codes. It helps healthcare professionals accurately assign E/M (evaluation and management) levels for different types of patient encounters.