Congrats on the 50% off sale!
Knowing WM, when it didn't scan in their system, I am guessing a worker had to input that name and price manually and then they had to put the stickers on them.
Checking stocktrack.ca, while I still can't get the instock numbers for any Joes to appear, it does say $15 at that lone ONT WM.
Normally when something doesn't scan at the checkout (and I have this happen a few times a year), they will add it by typing the proper name and price so that when the next customer buys one, it is fixed.