[int_19h]

The difference between the two is that a government-mandated registration scheme that mandates up-to-date status can clear a lot of legal bars that a private list compiled from random sources does not. Just because someone filled a warranty card for a gun 10 years ago doesn't mean that they still own that - or, indeed, any - gun today, and courts would generally balk at making such an inference for the purposes of, say, signing a warrant for a search.

[gigaflop]

I don't personally believe that the data would be good quality by modern standards. Also, with rising levels of minor paranoia among some groups, I'd wager $1 that people these days are less likely to fill out forms like the ones shown in the article.

However, if we presume that the data were of good enough quality and available to government, I believe that at least California would try to do something with it.