I've kept mine in the tub for just over a year, but I'm going to transfer it to jars because it is starting to dry some. The small tins are not good for long term storage. They'll dry out in about 3 or 4 weeks.
I assume you are talking about storing it long term unopenned. It will be fine; there is an inner plastic seal. When you do open it the lid seals fairly well, I have a tub about a year old and it has been fine to smoke.
I'm currently smoking EGR from a year 2000 tub. The tobacco was still moist when I opened the tub last Winter. Each time I need some, I put it in an EGR tin. I keep the resealable inner plastic seal in use, which is still keeping the tobacco fresh.
Every vintage tub I have smoked has kept the tobacco moist.