There's obviously only one way to tell for sure, which is to test an aliquot of what you have right now, but it's almost certainly good to go.
This paper is supposed to be a study of how well a specific chemical method (HPLC) is at detecting testosterone cypionate and its degradation products. They took cyp and then did all the things to it that you'd do to degrade a molecule: lots of ultraviolet light, heat, high pH, low pH, and then exposing it to a strong oxidizing chemical (hydrogen peroxide). They weren't specifically trying to tear up the molecule, but rather to simulate what a vial of test cyp might go through if the person who buys it is a little careless -- leaves it in the light accidentally, doesn't refrigerate it, etc. Just "normal" abuse.
TLDR - it holds up MUCH better than all of the package inserts suggest, both to heat and light. And, when you do manage to break it apart, you're most likely to end up with naked testosterone as a result -- no ester, but not a Frankenstein compound, either. If you were to inject some lightly degraded test cyp, then, you'd probably get a little bit of PIP, a faster serum T spike from the test, and not much difference. And, based on how degradation kinetics work, a simulation like this is probably a good proxy for a small handful of years.
I can't source this claim, so assume it's a complete lie, but I've read that a timespan of teens to twenty years leaves you with something that could get you by, but wouldn't be wonderful. I've been tempted to do more experiments in the lab, but there's only so much that I want to mix my professional life with controlled substances, ya know?
