Keep them. The most common reason is that they multiplied and spent all their energy doing that. That mens you get 2 blooms next year. Other reasons are too shallowly planted, too deep, leaves cut off too early last year, too dry conditions over year and the like.

Agreed, but would add that the only other cause of blindness in Daffodils is Narcissus root fly and that is more obvious than just no flowers. If the leaves are good and green then ok, but if the Narcissus leaves are poor and few, dig up the clump and examine the bulbs. If they are soft and squishy, open one up and you cannot fail to see the grub. Burn any infected ones, there is no amateur cure.

Many thanks - that's what I wanted to know!

Good point Owdboggy. It is not nice when you find grubs. The bulb will feel soft and will smell rotten and a white grub in it - yucks.

We used to have hundreds of Daffs here, but slowly the numbers have dwindled all because of this pest. There is no point replacing the bulbs as it is also found in Galanthus and we have 1,000's of them to act as a source.