It may be worth explaining here why there is this difference in the signs. I learned this several years ago on another Tesla forum from someone who is an owner of several shopping centers in a few states that have gotten Superchargers installed, so he has firsthand knowledge of what is going on with these.
City and state regulations have certain requirements about how many parking spaces there need to be per square foot of retail store space. At many/most places, they don't put in much more parking than they have to, because the store space is where money is made--not extra parking spaces. So when a Supercharger is being installed, if any of the spaces are marked for charging ONLY, by law, that can't still be counted as parking spaces for the retail customers, so it must be subtracted from the number of spaces per square foot of the store space.
So basically, there are almost no locations that are far enough over that ratio where they can spare to eliminate an entire 8 or 12 parking spaces out of their lot by marking them for charging only. They may be able to mark a few of them, but several will be marked for 30 minute customer parking too, so they can still count for the retail use.