Every gun bought from an FFL is recorded as part of the "permanent record" of the FFL. When the FFL finally goes out of businesses, those records are turned over to the BATFE.
Every gun bought from an FFL can be traced from the manufacturer to the first purchaser, and, in places like Kalifornia, to every later purchaser, unless the purchaser violates the law.
There's more than enough information to drive an initial wave of confiscations and it is likely that the vast majority of people who own even one gun have bought at least one through an FFL. This number will only increase with time.
Thank you for the info. As I thought, they have enough info to qualify it as registration and CCW list tends to confirm to ‘them’ which of us are armed.