Yes, you are definitely being too hard on yourself.

Buying certified seed only guarantees that the potatoes themselves aren't already contaminated with the fungal spores for various potato diseases. It is absolutely no guarantee that the plants grown from them won't get such a disease. The spores for these diseases are widespread in the environment -- whether a plant gets them or not depends more on its health, IMO, than on exposure, since they're all pretty much exposed most of the time from what I can tell. When you think about it, these spores must be everywhere -- each infected plant can generate millions to billions of spores, and these spores can travel for thousands of miles on the winds.

You could have planted certified seed and still had the same results, especially in such a wet, cool, and humid year as we've had here in the midwest.

I've had good crops from certified seed and good crops from grocery store potatoes, and bad crops from each as well, depending upon the year and the weather.

The main disadvantage of using grocery store potatoes is, as you stated above, the sprout inhibitors used on them. I've planted ones before which looked all ready to sprout, and had them sit for months without growing. Once they get to the point they are well-sprouted, with about 1/2 inch or longer shoots, then they'll grow for sure, in my experience.

Denninmi puts it well. With grocery store potatoes, you are hoping you purchased potatoes that weren't diseased. With certified, the potatoes have been inspected and tested several times to insure they do not carry disease. Either way, they can still get disease after you plant them if it is in your environment.

Some diseases will carryover on organic matter in the soil and may last for a period of years. Thus, if you plant diseased potatoes one year, that disease may keep showing up for years afterwards even if you plant clean potatoes after that.

Currently I have an infestation of potato scab in my garden which has made growing potatoes impossible because it carries over in the soil. As a result, I've moved my potatoes to difficult to work corner of a field about a 1/2 mile away where they are doing fine.

Denninmi puts it well

I'll second that beeone. Thanks both of you for replying. I had somehow gotten it into my mind, that I had "caused" the blight by planting uncertified spuds.

Denninmi: you really did explain that in a way that I could understand potato blight. Think I'll try again next year. I'd love to order some Yukon Gold, my favorite potato. Thanks so much.