Now that it's pretty clear what combination of EVSE maps constitutes a full picture, how about including a consolidated set of EVSE icons in the annual GPS disk upgrades. The disks are not inexpensive and this would increase sales. If the GPS disks include a software refresh like Toyota's, you could add EVSE as a GPS destination choice.
To add extra value, offer all Chevy dealers the option of listing their chargers as open to the public during stated hours. No other map will have these.
While the general issue of selling feature upgrades for existing models is unsettled at GM, the GPS disk upgrades are accepted practice and a good way to see if more features mean more revenue for GM.