I think daffs need the soil to be at least 6" deep. I used to have a garden where the daffs in shallow soil rarely flowered but those in deep soil flowered profusely. It may be due to the winter temperature profile that they experience. I would give them another year to prove themselves.
I've left blind bulbs in because I've seen advice that if you do this that and the other they will come back next year but they never do. I am making a real effort this year to dig up all those that are not flowering - yet again.
In theory, at least, as long as the bulbs aren't diseased and the cause of the blindness (such as a lack of mulching) isn't present again next year, they should start flowering again.