It’s my understanding that when they are processing a Form 4, its almost like when you buy a house. There’s a real estate attorney that does title work. Verifying that the property really exists, checking the title for liens, verifying that it is eligible be bought/sold, taxes are not in arrears etc. For a Form 4, there has to be a manufacturer that made the device with that serial number, a distributor who received it with that serial number, and sold it with that serial number, and a retailer who received it and sold it with that serial number, and then the end purchaser who fills out that Form 4.
I think a Form 1 is faster because there is no “provenance” to be traced/tracked. For a Form 1, you’re the ‘manufacturer’. So the NFA paper trail starts with you. Just my opinion.