The good and homogeneous looking seeds are from a cross of ((Royal China x (Assertion x Amadeus)). Normally there are no problems to get seed from such crosses of standard daffodils. More complicated it is to obtain seeds from crosses of standard daffodils with species. Symptom can be successfully crossed with N. tazetta, but the seed corns have different size and some don’t look good enough for producing seedlings.
In any case every daffodil enthusiast should make some crosses. It is a special joy to flower the own seedlings in five or six years.
Theo