? There's plenty of factory boosted Chinese rubbers. They even talk about it in their official materials.
I'd be wary of stocking up on rubbers, especially during sales. Often sales are made when rubbers are nearing their shelf life. They might sit in a warehouse for half a year, a year, maybe even two. Of course with new models you might also get one that was made less than a month ago.
Butterfly reckons an unopened rubber kept away from UV, heat, airflow etc. is good for a year to two years before the performance degrades. This includes the storage time in the warehouse! You might not have any clue how long they've been sitting there. By the time it's in your hands you might not have a lot of time left.
So I don't know. It's probably best to buy fresh sheets and glue them on immediately, but I usually keep one or two replacements on hand and just pray. I also seal the package additionally behind another layer of zip bag, just to add some insurance. You just need to watch out that there's not moisture inside when you seal it. The best should be a bag with a black matte outer coating and a foil coating on the inside, but I'm sure a transparent plastic is probably fine. If you're really serious you'd induce a vacuum in that bag as well. I'm not sure it matters really.
Bear in mind rubbers will age from internal mechanisms even if stored reasonably. The bonds will rearrange themselves constantly even if not subjected to air or light. Table tennis rubbers are very dynamic and often under tension so it's probably more dramatic for those than for like a washer or something. For simple rubber products the estimated shelf life is about 5-10 years, but I'd expect less for TT rubbers, but I could be wrong.
