>>Whether off the street, from an FFL selling illegally, or stolen, they are still obtained illegally and neither the proposed law, nor any database of legally obtained weapons of which those would not be included , would stop that.
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>You're not really attempting to convince me that having a database would not help solve crimes are you?

This is the old IT conundrum... how to acquire the data, once you've established that it would be nice to have them. And the scope is staggering in this case, specially with the most important (I'd say mission critical) part of the data being off the screen.

Just imagine you want to build a database of all bridges in the country. First, you may have some data in some databases already. You may even have a way to get these data (which involves negotiating with their holders - rights, formats, definitions, lookups for various discrete-valued fields). You may have some kind of organization which will work on acquiring the missing data, and may even be sufficiently smart or lucky to have some consistency in all of that. Still, you can never be sure whether the definition is respected throughout the database. You may have bridges which no longer have a river beneath them (we have one in our city), you may have bridges which still don't have a river (we had one, and then they diverted the river to flow under it), you may have unfinished or semi-ruined bridges, you may have bridges which don't serve any traffic any more, you may have private bridges which cross the streams on private property, bridges which are purely decorative, which officially don't exist... the borders of the definition are porous.

I guess any large database must be partial. Anything that should be in it may be actually absent, or just plain wrong.

And then they churn statistics out of those, and say that "numbers don't lie". Of course, whichever calculation you perform on them will give the exact result that the mathematical operations on those numbers should. And the numbers are correct, in a sense: there's exactly that many of those in the database. It's the "those" and "in the database" that are frequently wrong or skewed.