I emailed and asked the ATF myself. I can't really find the email right at the moment, but here's the short answer:
The bound book is a record of all curio and relic transactions while the license is active. Not necessarily a record of what you "used" the license for, but a record of what happened during that time period.
Purchase a C&R firearm in interstate commerce? Log it.
Already own a C&R from before? Don't log it.
Buy a C&R locally on a 4473? Log it.
Sell a C&R firearm? Log it.
Sell one from before? I'm not 100% sure, but I think you'd at least log the disposition (this is the only question mark I have).
Many are hung up on the idea that it's only what you "use" the license for, but there is no provision in the law making a difference between stuff you bought using it and what you bought locally on a 4473. Log what you buy or dispose while the license is active.