And their level of compliance is what?
Among criminals, I'd say it's a safe bet that the compliance rate was 0%.
"Criminal" is a poor choice of words there. By definition anyone who failed to comply is a criminal. Whether they willfully chose not to register, never know of the requirement in time, or otherwise.
Who and what is a "criminal" changes with the stroke of a pen. I think you meant "criminal predators".
The estimated number of such firearms as defined by legislation is much higher than the number of such firearms which were registered.
It is safe to say numerous illegal firearms are held throughout the state.
They find them all the time during other investigations, failure of payment of storage or similar bills causing them to come to the attention of LEO, or after natural disasters expose some.
Those who registered them are now an easy group to target with legislation, they become a smaller percentage of the population as the population increases. Transport restrictions for such weapons is high. Most legislation introduced to target such divided and conquered segments of the community will receive only token opposition, because it does not effect most or a growing portion of the community.
Parts and components become more expensive because the wholesale market shrinks dramaticly. Everything becomes custom. With foriegn import restrictions in place, that means formerly cheap weapon platforms become expensive to own and maintain with national level restrictions.
Once only grandfathered individuals have something, they and those firearms can be demonized as the population grows ever larger. New shooters are not exposed to such firearms and the myths surrounding them on a regular basis. Those myths grow larger and larger, and owners of such weapons viewed as more and more extremist.
So such demonization starts to make sense, and such bans and as a result future restrictions begin to be more logical to the next generation. A new weapon platform becomes the demonized catagory as a previous one is defeated.
What are the new platforms targeted? All semi autos? After all they are only cosmeticly different as they are told all the time.
Pump guns too? Made sense in Australia and the UK when they restricted semi-auto out of reach of most.
Guns considered "too powerful", or "too concealable"? Also made sense in places with minimum sizes of pistols and increasing caliber restrictions. The list of what is too powerful grows.
They can initialy be grandfathered with conditions, and those conditions can make you and the community easier to defeat later.
It also damages your ability to use such firearms for defense in the future. Much like using a select fire weapon today.