Kept cool and dry, coarse fir bark will probably outlive you.
I bought a lot on sale two years ago, and I'm still using it.

I have numerous dead fir trees that have been standing for 50 to 100 years. The entire tree EXCEPT the bark has been completely consumed. I run the slabs of bark through my chipper/shredder and then screen to size. I buy from Ace Hardware plastic storage tubs of about 15 gallons, when they are on sale. I have 6 of them filled with bark that keep beautifully. Some will be part of my final estate. Al

up next,
90Gal premium Aged FirBark, painstakingly-sorted, and in Premo condition, packaged to go,,
lets start at $50.00,, can-i-get-a-fiddy, get-a-fiddy_get-a-fiddy, do i hear a fiddy-five..... :)~

I would agree... kept at average temp and dry, it should last a good, long time. I've had unopened bags of ReptiBark sitting on a shelf for 3 years, and it's fine.

Be sure to wet it thoroughly before planting in it. I like to soak it for a while so it absorbs moisture and doesn't dry out too quickly when first using it.