I would have to disagree (not totally, but somewhat) with the "difficult to prove you got it after Dec 1 1998" part. I think in many cases, it wouldn't be overly difficult to prove at all, but time consuming for the research required to make a solid case. Acquiring the said proof would require a lot of time and effort (which translates to money) and weighed against the chance of failiure to convict, it's way more effort than it's worth considering the minimal impact a "positive" outcome will have. In some cases, it would definitely be impossible to prove one way or the other. The end result of this is the same as if they couldn't prove it.
But in the end, the trade of airsoft is being largely ignored by law enforcement at the moment, and that's for the best. If that will continue in the future or not is unknown. As Honestjohn said, let's just enjoy the freedom we currently have, without getting too comfortable with it, because it could end any day.
I think this post was long overdue and clears up a lot of misconceptions (for me along with many others, I'm sure). Thanks for posting this. It was very informative, and I'll be referring back to it often.