Posted: 26/03/2016 at 14:16
The vast majority of narcissi self-propagate by developing new bulbs underground and these are clones so are always true to type. Crossing can occur, but will only affect plants grown from the seeds. Narcissi seeds rarely develop and even if they do and go on to germinate, they will take several years to produce flowering bulbs.
Basically don't worry but if you want to be 100% sure just make sure you dead-head all of the flowers when they go over.