The established law started with "No new 'hi capacity'* magazines."  In 1994ish.  I may not have the date exact. Doesn't matter.  I'm lazy, look it up if you care.
(*Standard capacity for the weapon redefined as "high capacity" by a bunch of legislative faggots with no technical knowledge and no other credentials. About like claiming any gas tank over 5 gallons is "High capacity.")
Then it was "No repair parts" and "no spare parts."  Because that was a loophole* you could drive a semi through, and people did. Some companies marked production dates on their mags for this and other reasons, which helped ID the "Bad" ones.  Some weren't produced until after that deadline.
(*A "loophole" means "we're ignorant shitheads who didn't actually say what we mean, and for some reason, people and the courts are going by what we said." Sort of like that crazy chick who expects you to understand what "it's fine" means.)
Then it was, "Turn them in to be destroyed."
And an injunction.
And a court ruling, rescinding all of it. The entire fucking law.
Which means, even if it was only in effect for 90 seconds, and so far it's at least 90 hours, ANY MAGAZINE made between 1994 and the present can legally be brought into CA, whether or not it's marked any particular way.  And even if they get an injunction against the injunction, followed by winning a case against the case they just lost, all those magazines will remain grandfathered legal in CA.
And because there is no way to distinguish those magazines from any other identical magazines, anything found in CA with that production date range must be assumed to have been legally acquired in this window.  If residents bring in 10 million more magazines made between 1993 and X, and don't get caught, once in CA, the burden of proof will be on the state to prove they were imported after X. Which hasn't happened yet and may not.
So even if X happens and Commiefornia manages to ban them again, using different language, the billions of mags in the state will remain legal, and CA will have to start from scratch down the road of fascist cocksuckery.
And they even admit so here: http://michellawyers.com/wp-content/uploads/2019/04/2019-04-01-Defendants-Ex-Parte-to-Stay-Judgment-Pending-Appeal.pdf?fbclid=IwAR01_1K_OqyVrZhiHGCh3fzKnDwqydLg1g1UfcAXIEwHV9ddwa7_JLnNFRY
Watching hoplophobic faggots squirm in agony is almost as delightful as watching fetus fetishists be told for the 48,972nd time that Roe v Wade is established.