Talk about red flags...
Most of my NFA collection was stolen in 2011. The day it happened. I reported the SN's to my local PD, ATF and sheriff.
2 PD detectives came to my door a year later. They notified me that 2 of my cans were recovered in a sting in Atlanta 7 days after the theft. I wanted to know why the ATF did not notify me about the recovery for over a year? The detectives said, the ATF thought I sold my stuff under the table because the serial numbers were not reported stolen in the NCIC.
I showed the 2 detectives a copy of the police report CRN with the serial numbers, printed email notices to the Sheriff, ATF, my insurance co. and the BOLO created on 3 websites. They were speechless. None of the LE agencies entered the SN's into NCIC for more than a year. Even after that, it took another 2 attempts to get the correct SN's into NCIC.
Buy what you want.
The ATF seems to care about multiple purchases only if the info can be used to justify or compound charges in other investigations.