Question 21248/21249 Guidelines

Looking for guidance on CPT codes 21248/21249. I am searching for a specific policy or guideline that states how many implants are billed for each code. The code description states 21248 as a partial reconstruction and 21249 as a complete reconstruction. My providers and I have always billed dental implants as 21248 for 1 - 3 implants placed, and 21249 as 4 or more implants placed. I have found other forum threads that reference the same billing method however am looking for an official rule.

Thank you!