Definitely works in reverse like you say (in terms of routing, not point of origin, obviously), but not on the specific dates I needed. I consider myself really lucky if I can make these offers work in conjunction with fixed dates. As it happens, I arrive one day late (rehearsals at the beginning, concerts are later on, fortunately) and will leave one day later.
Anyone one else had any luck booking this deal, either to one of the lesser known Chinese cities in the offer, or wrangling it sideways to a more mainstream destination as I did? On the KLM Swiss page, the offer to the Chinese cities is bookable until 28 February. For other points of origin, it can be different, I think.