BTW, few give a rats ass about this law. Guns stores routinely sell high capacity magazines. The law was written by liberals who are notorious imbeciles and it says if you already have them then you can keep them. This means since magazines do not come with a date stamp that all high capacity magazines are legal. I’ve bough multiple firearms with magazine capacities beyond the Colorado idiotic limit.
Some plastic mags do come with a date stamp right down to the day and hour of manufacture. I bought a bunch of plastic 20 rd. and 30 rd. SKS mags before the new law. That should actually help me if they ever tried to prosecute me.
It also means you could shop online or at gun shows specifically for pre-July’13 mags.
FWIW none of my steel mags have dates and your point is well taken on that.