When I first bought my pipe, I bought a bag of pipe tobacco. It was a small ziploc bag. I kept it in that bag for about two months, then transfered it to a Ball-brand jar (with a rubber gasket seal.) I read recently that tobacco only keeps in ziploc bags for a few days. Does that mean my tobacco has gone stale?
As a non regular pipe smoking phlosphr I’ll ask this: Does the tobacco taste hard, harsh, dry, pinny? Or does it taste fresh, smooth, salivating?
Of course the later would be the ideal. I’ve had my captain black pouch go bad, but then again, as I said before, I’m a non-regular pipe smoke’in man. I like a good smoke when the night is crisp and the leaves are falling…Same with a good cigar…You just know when the tobacco has gone bad…
If you happen to smoke cigars, too, put the pipe tobacco in the humidor. If not, just put a slightly damp (not soaking wet) piece of cedar in the Ball jar with the tobacco. I got that tip from a tobacconist, and it seems to work very well.
Put a slice of apple in the jar and that will freshen the tobacco.
I read that this creates mold and fouls up the tobacco.
Yes, I would not use the apple. Always use some sort of humidor or climate controlled contraption. 
Woudl the freezer or fridge be a bad idea?
I bought a kilo (2 and a bit pounds) of rolling tobacco some time ago and a friend told me to bag it into smaller lots and keep it in the freezer. In my experience it keeps the tobacco fresh for at least a few months.
To address the OP, probably yes. (You’re going through it pretty slow if you have a small bag for two months. But anyway.) Plastic bags are not air tight, even though people assume so. Next time you slice an onion, put half in a plastic bag of the brand of your choice. Then hold it near your nose and you will have little trouble smelling the onion. (I have one of those vacuum sealers, and those bags are about as air tights as plastic bags get.)
Drying out is only part of the equation. Just like foods, tobacco can go stale just by sitting around minding its own business. It has chemical components that break down, oils that can go rancid, etc. Plus it can pick up off odors from the air.