As supplements/drugs age, they loose potency, they dont become rancid. It is more like a best before date, then an expiration date. The T3 is still safe to use. How much potency is remaining in the product is impossible to determine without testing it but I would guess it would have a 80-85% potency of the original amount.
Just a tip, T3 is your body's thyroid hormone. It won't do anything for prolactin levels. To combat high prolactin levels from tren, you want to be using a drug like cabergoline. 0.5mg E3D is a good dosage.