How can I get my nook books back?

Every time there’s a new update on my iPad mini for nook app, it seems that I keep losing more and more of my ebooks in my nook library. I mean, a lot of them I’ve started buying from maybe over 10 years ago and I probably had over 3000 books. But every time there’s a software update, I lose books. Now I’m down to 2000, and I know I’ve lost a lot because I actually had to repurchase some of the books from my favorite authors. When I went back to purchase history on my Barnes & noble account, it only goes back as far as a quarter of the year, so those books I bought from then are still in my library. This is stealing in another form! I already bought and paid for those books, and it just disappears!!!