Yup, half of mine didn't come up last year. I thought I'd lost 'em, but there they are!
I also thought the corms were only good for one season. If only I'd known - the number I've thrown out!
I now have a theory, though (stand well back!) - I think it depends on the size and maturity of the corms. I reckon that, like bulbs, they need to reach a certain stage before they'll flower. Hence my no-shows last year popping up now.
And in future, I'll also ignore the pack instructions about the corms beng treated to last only one season.
Better go now, I feel another theory coming on...
;D