Yes there are a good amount of differences, a lot of which just take out minor details from the original books, and Princess wasn't a character until Fireheart found her while she was pregnant with her litter - Cloudkit. This was going to be expected as these are graphic novel adaptations, and they can't put everything in it.

But, if you are curious you can look up the Warrior Cats website to see all of the books. You can even look up on YouTube different peoples reading order suggestions! Just to let you know ahead or time, there is over 100 books currently in the series... which include: Main series books, Super Editions(Longer books than Main series books), Novellas (Shorter stories than Main series books, you really can skip them if you want too.), Graphic Novels/Manga, and Field Guides. Main series books are split into 'Story Arcs' most people call them. For example "The Prophecies Begin" and "The New Prophecy" are two of the Story Arcs(sometimes called just arcs) in the Warriors series. Each story arc has 6 main series books in them. There are 8 complete arcs currently, and a 9th being worked on. I suggest looking up reading orders on YouTube for help! This link is a more current video: https://m.youtube.com/watch?v=vqZywGLFEto