https://www.atf.gov/firearms/qa/does...cquisition-and
Nope. Overnight, it goes in the bound books and they have to have an FFL. So, the COMPLETED lower must have the relevant information engraved on the lower to be entered. No info, it can't be kept. The owner has to stay with it. 80% shit boxes didn't exist before the requirement for serial numbers. They don't get a free pass as pre-68 guns do.
You are absolutely giving out the wrong information and you need to stop before some unfortunate person believes you. You don't have to believe me. Call the ATF: Industry Operations (303) 575-7640.