I think you'll get the PDF once the campaign ends. I think that's how they did it before if I remember right.
And yeah, they don't change the rules really at all. They change the covers, maybe change some spellings and what-not. About the most reliable thing they change around between printings is what adventures are included in the back. But they are like 99% the same book.
The most notable difference is if you happen to have a couple of first printings like I do, they don't have an index. Which is...not ideal.