I've done some research on this. Not an extensive deep dive though.
Typically, the resin is to remain air-tight until usage. I recently had a large bag of mixed bed media come in with a broken seal, but was inside a second bag. I still required a replacement or a full refund.
Can you use it? Yes. Just keep an eye on your TDS output and expect there to be some decrease in performance. How much of a decrease though? I have not dived deep enough to get a good opinion.
I have been trying to find some specific data, regarding the various types of resins changing their charge when exposed to air for extended periods of time. I think for our type of usage, the ionic exchange difference would be indistinguishable. But that depends on quantity and quality of air exposure during transit. I hope that makes sense.
In the nuclear industry, chip making industry, or other similar industries that require perfectly clean water, there are normally regulatory requirements to their water filtration. From what I have seen is pre-filled resin cartridges with virgin grade resin.