There is still on occasion a problem with the date added being changed to that of the imported .opf file, as referenced in this thread:
https://www.mobileread.com/forums/sho...d.php?t=122692
Specifically, it seems to occur when I add books to the library then edit the metadata in bulk. Most often, when I do this, I'm just changing something simple like the "authors" field - no other changes. When I exit the bulk editor, though, I find the dates of books with epub or mobi formats in the mix (not sure which of the two, might be both) have changed to the date that was in the opf file in the original directory. I had understood from the thread that this was old behavior, so I thought it might be a bug.
ETA:
OK, I just saw it happen again - this time, without the bulk metadata editor. I added a book in 3 formats from a single directory - epub, mobi, and txt. The expected automerge popped up telling me that the books had been merged into one entry. The date added, however, was for May 2010 - the date from the original opf file. The "date modified" custom column shows today's date correctly.
This is calibre 7.54, Win XP 32 bit.