Buttercup?!?!?

It's that time of year again. The "Pheasant's eye" always late to open.
For some quaint reason biologists never seem happy to adopt a name and stick to it. 
Things I once bought as Amaryllis now seem to be sold as "Hippeastrum".
I remember hearing Mam distinguish between Daffodils, Narcissus and Jonquils.  
(If anybody else needs to know "Why Buttercup?" - follow the link)
I, finally got a "Round Tuitt" and looked them up.
Apparently it's a case of "Same dog, washed." But I'm not aware of any of that family/genus flowering any later than these.