Quoted:
I have an 01 FFL I received in December. I'm listed as sole proprietor. If I wanted to sell a
gun I had in my collection years before getting the FFL would I have to enter that gun in my
records and then sell it only after a 4473/nics check? I think I do have to.
View Quote
As mentioned in reply to your thread in team, no. You may and ATF would like you to, but you are not legally required to do so, at least not by federal law.
Ditto for any guns you transferred from your bound book to your personal collection at least one year prior to the date of sale/transfer.
It's in the FAQs at the ATF website, which you should really already have read and more or less memorized, along with the FFL handbook and guide to published firearms laws for your state, which ATF has sent, or will send to you.