Cultivars that are no more

I beleive over the years many of fine cultivars simply dissapeared. They might still be in culture as lost labeled plants, but can you buy

Nightwood

or

Aulis

.... anywhere?!

Can we make a list of plants that are most probably no longer in cultivation nowadays?

Even more difficult: could it be that some cultivars have disappeared because they were mixed up? Meaning, some plants with a certain name are still around, but they are wrongly identified and the original plant with that name no longer exists ...

I think that not all cultivars are equally "unique and special", some are just "one more of a range of similar plants". If these clones would not have gotten names, no-one would ever notice them. When such a cultivar "disappears" we lose equally little as when a no-name plant is tossed to the compost.

To me it is a more interesting question how we can determine the relative value of all those (still) existing cultivars. Which ones are most important to keep growing? Everyone will give a different anwer her, but I am anyway curious for opinions!