daffodil question for a neighbor

i was just chatting with a neighbor and they have a dilemna, i am hoping someone here might be able to help.
they have a raised bed that they have done this to twice too.
they planted 70 daffodil bulbs. the first spring they came up beautifully, they allowed them to die back naturally, doing the feeding thing correctly. they then planted zinnias during the summer, to hide the folliage and for summer interest. the following spring only about 6 clusters of daffodils came up. this has happened to them twice. they have dug and there are no bulbs there.
what could have happened to them? i'm stumped but i'm no expert.
any ideas would be welcome.
thanks.......

Could be a Narcissus Fly attack

http://www.agri.gov.il/Envir/narcissus/narcissus.html

a major pest when daff are grown en masse

I would strongly suspect squirrels. They routinely dig up many of my bulbs and re-landscape the neighborhood. Dogs, raccoons and children do the same.

Daffodils are poisonous, so they are not consumed by herbavores, but many animals put them in their own cache to the gardener's dismay!

On the brighter side, I have been the recipient of several new bulbs from my herd, things that I know for sure I never bought or planted, they just showed up one day! Very possibly one of your neighbor's neighbors is enjoying the daffodils, wondering where in the world they came from!