I’ve heard breathing through the pipe for a while before lighting it will help moisten the tobacco, too.
Yes, blowing a few breaths through the bowl will rehydrate the tobacco if it’s a bit on the dry side.
But if it has been sitting for years in a tin that isn’t airtight it will dry thoroughly, and taste harsh.
Even though leaf feels crispy to the touch on the outside, the leaf can retain some moisture internally.
The oils in tobacco can remain in good condition for quite a while longer. Provided the tobacco is stored in proper conditions. Heat, overly dry conditions, exposure to the sun, will accelerate the drying of the oils. Once that happens, you have mummy dust.