Unfortunately these flag's documentation is a bit "brief" and some are only used internally and/or are only valid at certain points in time. Next problem is, how is IsDirty() supposed to find out, who you are and when you called it last time (yes, in theory it would be technically possible, but I doubt also feasible)?
I'm not a hundred percent certain (the PluginCafé certainly can give you a better founded answer), but I think, you won't get away without iterating the children yourself and storing/comparing the result from GetDirty(). You should also find lots of discussios already on this topic over in PluginCafé, you probably wouldn't even need to wait for an answer on your own question.
Cheers