Do you mean never seen the bendable seeds? They happen quite frequently, it seems. Composite (to which marigolds belong) flowers are a composite (hence the name) of many tiny florets. I suppose if not all of them got pollinated, then not all of them will form viable seeds. It also seems that the proportion that gets pollinated can vary dramatically from one species to the next. Marigolds tend to produce lots of viable seeds. Stevias produce very few (proportionally), as do celmisias (about 90% of seed packets of this genus I get are completely devoid of viable seeds for some reason, and those that do have viable seeds usually contain only about two or three viable seeds). I guess it also depends on how often the flowers get visited by pollinators. Hope this sheds some light on the matter.

Hi,This interests me and I have heard two directions for colecting one states to take plant just when it's faded others say to let the bloom dire compleatly on plant befor colecting.
I also would like to add that I bougth some poor bendable seeds on ebay my own seeds are jet black and sturdy however to my bigg suprise they no name seds germinated just as well as my thomson morgan seeds.Keep in mind soil temp and moisture level I always start indooors so I can controle both of them.

if you collected seeds from a hybrid plant they would not have turned out like the parent plant anyway.

I think it's best to let them die completely on the plants before pulling off. My kids though arn't quite that patient and have decent luck planting ones that haven't dried completely. I guess my point is that it may not really matter. I just try not to let thsem freeze.

Here is a link that might be useful: Marigold Seeds