After my research on making peelable hard boiled eggs, I did a few experiments.
First I tried the salt theory. One dozen eggs separated it into two groups of 6 and, in two pots, I performed the standard method with one pot having added salt. Nearly two tablespoons for the 6 eggs. I can report that there was absolutely no difference in their peelability.
The second experiment was to take 6 eggs with the store pull date of March 2 and 6 eggs with the pull date of March 20th. This experiment I performed on March 18th. I boiled them using the standard method (a Sharpie(tm) writes on eggs and it doesn’t come off through boiling, by the way). Here, I notice a difference. The older eggs were easier to peel than the newer eggs. Not a lot easier, but it was noticeable.
One data point.