I think the issue is with using a multi-dose vial, rather than degradation. Normal protocol is to discard after 28 days unless stated otherwise (so 30 days in this case).
I've copied this:
With injectable medicine you’re bypassing your stomach, lungs, and skin, and injecting directly into your blood.
This is the reason sterility is so important and why you must be concerned with how long you use a multi-dose vial. When the product leaves the pharmacy it is sterile. This is known because of all of the rigorous standards during production mentioned above. After you receive the product, puncture it, and begin using it, there is a risk of introducing germs into the vial. Germs introduced into the vial can multiply in the vial and end up in your blood the next time you inject. It doesn’t matter how careful you are, we are surrounded by germs, there is no way at home to be absolutely certain you didn’t contaminate the vial – but sterile production standards, and added preservatives help protect you, for at least 28 days.
Remember the goal: keep germs out of your blood.
People often struggle with this concept as it relates to sterile injectable medications. We go about our everyday lives, get sick, get better, and we minimize the importance of keeping our blood free of germs, because our body does the job for us. However, if you are injecting medications, you need to be more aware of sterility and safety.
People will sometimes say, “but I used a vial well past 28 days after first puncture and I didn’t get sick, so why should I care?” Well, those people are taking a risk. Just because you didn’t get sick by risky behavior one time, doesn’t mean you will never get sick if you continue to disregard the rules.
Using an injectable medicine beyond 28 days after first puncture is risky. It is not recommended by the scientific community, and not recommended by the pharmacy that made your medication.
I'm not so sure about risking it now! Would maybe go to 35 days but definitely not beyond.