I still don't understand why 23+ year old magazines have ANY value whatsoever...in any state!! The 1994 federal AWB is gone gone gone, never to return.
The federal law pertained to newly manufactured firearms and magazines. In addition to the federal AWB, some states passed their own laws covering so-called assault weapons and magazine capacities. These laws were piecemeal and generally addressed if and how people could buy, sell, trade, or possess pre-ban firearms and mags.
Following passage of the Clinton AWB, we saw states like CA and NY develop their own rules that were based on the federal law but went further than it did.
For example, the Clinton AWB did nothing about stuff people already owned. Those firearms and magazines were grandfathered in, increased in value, and could be freely bought, sold, and traded under federal law. In contrast to federal law, CA passed laws requiring registration of firearms it defined as assault weapons and banned intra-state transfer. Later, it passed a law that allowed people who owned pre-ban mags (mags manufactured before a specific date) to keep them but forbade people from buying, trading, or obtaining pre-ban mags via gift. Before CA changed its laws, it was common for Californians to buy pre-ban mags online. -Compare that with NY's law that banned newly manufactured standard capacity mags but allowed people to buy pre-ban mags until some relatively recent changes.
When the federal law expired in 2004, the various state laws remained in effect. Pre-ban mags lost their premiums in states that had no laws, but retained them in states where they were controlled by state law and could still be bought, sold, and traded.