I assumed (but have no proof) that the ditching of paper cassette labels coincided with A&M's move to recycled paper for its LP inner sleeves.That certainly is possible. I've never seen a timeline for cassette labeling with A&M. Some had AMPEX on the paper label, others didn't, and then the tapes with the printing right on the plastic. It kind of makes sense that they would find it less expensive to print right on the shell, and that it might have followed the tapes with the paper labels.
I always thought the black A&M 8-tracks looked very cool. Sorry to hear they were unreliable. Mike, were there similar issues with other colors? If I recall correctly, most were white until A&M went black, and then suddenly a lot of labels were using a lot of colors.