Over the years I've dealt with a lot of very old seeds and some years I think I see a correlation with seed age and blind ones, and other years not.
Same comment for stuck seed coats.
Other than tricots or similar, it would have to be an abberation of the same gene, or a similar gene that causes a blind seedling and I have problems accepting that it's always a specific phenotype that would result on all blind ones that appear whose origin is there b'c of seed age.
And no, I don't have any better suggestions to explain the phenomenon.
The other association that I've made and so has Darrel (Fusion) is that the seed viability of heart shaped varieties is not as great as non-hearts and that still holds for me.