It's probably new versions with the same content. If you mention which books and which publisher maybe someone can help you better.
However if the test style/content hasn't changed then I wouldn't worry too much.
The other option is if a local bookstore has the new versions and you can have a look without the obligation of buying.
Tinkers, the CSSE test has changed since 2012, in that it now consists of a one hour English paper with a bit of VR and a 15-mark continuous writing section, plus a one hour maths paper with a few NVR-type questions. As opposed to a 40 minute English paper / 35 minute maths (both written in-house, which hasn't changed) / 50 minute GL VR paper. The comprehension is pretty much the same; the continuous writing seems to be of the 'Describe how to make a piece of toast in 5 sentences' type (two pieces to do).
(The main difference, of course, is the dropping of the GL verbal reasoning paper, which in our house would occasion one 'hooray', one 'Oh. I liked that paper' and one expression of total indifference, I suspect. I think there were comments this year about the English paper including VR questions of a hitherto unseen variety? - to which I would only say, 'good'. It's called 'verbal reasoning
', guys - that means working it out