generally, unless otherwise stated, newer versions are compatible with old saves. the last version that was planned to break compatibility was 31.00 version, or the first df2010. 34.02 broke compatibility too because of a save corrupting bug with 34.01, however, many of the features and bugfixes usually require a regen, so you might miss out on some stuff. hopefully not minecarts
E:how did i miss so many ninjas?