I got a couple of boxes of never-issued Adventure Line magazines from about 1970 vintage. So far I've only run into two negatives with them.
1. The little rivets on the front hung up in my CAV-15 Mk2 lower and prevented the magazines from dropping free as they should. Cavalry Arms suggested using newer magazines without the rivets.
I instead used a rat-tail file to make a slight groove inside the magazine well so the rivets would have clearance.
2. The springs feel distinctly weaker than the springs in new C Products "AR-Stoner" 20-rd magazines. I have had a few malfunctions that might possibly be linked to weak springs, but they're sporadic and I'm still investigating that. I have also ordered a few Wolff extra-power magazine springs to test and see if that makes any difference.