I'm using iTunes to sync my photos. I do use photo stream as well and have have turned it off and on to see if it made any difference but it didn't. Ive even freshly synced my photo library to my iPhone and iPad via iTunes, but none of the date changes are copying across.
I only went into the package out of curiosity and would obviously never change anything within there (not long ago iPhoto would direct you there to see the originals - surprised they even let people do it!).
Im still deliberating whether or not to go to iCloud photo library, who knows.. perhaps the dates may show up correctly with that. But at the moment they're not using the traditional route 😟