…unused coffee in plastic… My intuition is that whole bean coffee would be okay to brew, but if it’s ground coffee I’d toss it – unless the quantity is large enough to pose an economic issue. Justification: When you grind up beans the already-large surface area increases by a huge factor, enhancing its ability to absorb chemicals (bad flavors, plastic BPA toxins, etc). Meanwhile the “micro-terrain” of the grind is more conducive to growth of mold & other microorganisms which, even if it doesn’t make you sick, might alter the flavor. No doubt temperature & humidity play a role, cool & dry being best. So much for theory & hypothesis.
Might I suggest you brew a cup & take a sip? A little field research lol. Cue spit take…