DI has a shelf life of about 6 months normally. If you make sure it is vacuum sealed such as with a Seal A Meal device or is unopened and still vacuum sealed from the vendor and stored in a cool, dark place such as the frig it can extend that up to a year in some cases. It all depends on how fresh it was to begin with, how well it was packaged (vacuum sealed in unopened mylar foil bags is great), and how well it is stored. I found buying bulk resin was not the answer for me since it exhausted before I could use it up. Now I buy better, fresher resin and in individual sizes or prefilled cartridges and it actually works better and lasts longer than what I was buying before.
I pack my refills dry by adding resin to the top, tapping it on the table or counter to pack it down, refill, repeat the tapping then do a final top up before adding the foam donut and screwing the lid back on. The resin should already contain enough moisture to hold it together, if not it has dried out and lost its cation and anion electrical properties.