Ok, so this is pretty bizarre... Entries from 2016 are NOT displaying when searched for in the admin panel. Whether we search by the year, title, or part of the title, until they're edited (using the id to access them).
I see entries from 2015 and 2017 but only a few from 2016 which, as I said, are the ones we managed to edit.
This happens in the list of entries as well as on fields that link to them and we've got LOTS of entries...
UPDATE - Check this out:
Articles listed from December 2016: https://www.dropbox.com/s/o0rmkiazm436etb/Screenshot%202017-10-22%2009.16.07.png
Searching for name of article: https://www.dropbox.com/s/ydwilwz6pye1jb4/Screenshot%202017-10-22%2009.16.44.png
Searching for year 2016, bottom of results, all 2015 and 2017: https://www.dropbox.com/s/w7imwnnfyrnjjri/Screenshot%202017-10-22%2009.17.15.png
If i access the article highlighted on screenshot 1, via URL: https://www.dropbox.com/s/opdv12hpyz993z4/Screenshot%202017-10-22%2009.20.50.png
The articles are there, they're accessible from the user end, but for some reason they won't show up on the Admin side. Bizarre...