User blog comment:PikovajaDama/Pre-release content on Dishonored 1 pages/@comment-1500935-20160626110343/@comment-16241899-20160626112503

In general, I don't think a subheader to mark D2 is necessary, as we do have pre-release and promotional pictures for D1 in some of the galleries as well, marked as such in their captions. Unlike information in articles they are not to be removed when it turns out what they are showing did not make it into the game, though, rather showing "during development there was also this".

So, putting D2 related images under the general gallery is fine, and for the sorting I  would stick to the concept art, in-game, additional, D1 first, then D2... so basically D1 concept art, D2 concept art, D1 in-game, and so on...

As for the special case of overflowing galleries because of large influx, a separate D2-related gallery would be an option but we could just as well make a separate gallery for concept art as is present on Corvo's page, or anything that would fit. I think that is an issue we can fix on a case to case basis should the need arise.