The Priority Club website only gives you an option to see your account history back 6 months. But it turns out the data is all there, the website just doesn’t give you an option to query for it.
A Flyertalk member posted a link that will allow you to go back farther. I can see my redemption history back to 2004, and my earning activity back at least to 2008.
Note that you’ll be asked to sign into your account, of course.