Episodes from 2016-12-19 and onward for The Late Show with Stephen Colbert are present on the site Calendar, but not the shows episode list or the API results. Seems like a bug of some sort :)
Those are specials, and listed as such.
So not a bug, a feature.
They were listed twice, as specials and as regular episodes, but they are specials, so the regular episodes were deleted.
Ah I see, thanks!