Hi Dave,
Supposedly sometime after Quantegy bought the Ampex tape brand, the binder formulation for 456 was changed, and no longer prone to SSS. I have had a couple pancakes of Quantegy 456 that were perfect, no problems at all. I'm not sure anyone knows though exactly what date the change occurred though. Quantegy 456 is a bit of a crapshoot I'm afraid, and of course Ampex branded 456 is either already bad or going bad.