Setting specific date of seeing for episode/movie BY API
I got asked about this feature and got response that I can do this by /sync/addtohistory method.
But this is obviously not the case, because such method only adds RATING to something I've seen in the past.
I can see one episode several times and in web interface I can add specific date of each watch - choosing between "today" "day release" "specific date".
What I see is discrepancy between functionality in web interface and in the API.
If Trakt.tv is meant to be our way to archive what we watch from several sources this is MUST HAVE and I am surprised there is no such function in code. After all I don't rate every episode I watch, often I just watch.

Yes, the /sync/history method support this. You just send a watched_at date as documented at http://docs.trakt.apiary.io/#reference/sync/add-to-history/add-items-to-watched-history.