it turned out that these books were 10+ years old and especially in the Air Law, quite a bit has changed
Good point, although it seems that sometimes the Air Law exam papers are out of date too, e.g. regarding the changes to Rule 5 in 2005. Having a 2004 issue book was acutally an unexpected benefit in that respect. But obviously if you only have one reference source available, it's preferable to have an up-to-date one. Knowing what the rule used to be might be good for getting the answers the CAA want, but not so useful for practical flying.