Mexicowanderer, the data I received from Pemex completely explains something I couldn't understand this winter season - places which usually report lots of sulfur-in-fuel related issues, with many owners needing rescues, haven't reported a single case this year. This includes Puerto Vallarta, Lo de Marcos, San Miguel, and Mazatlan. Now that I have the Pemex list of stations carrying ULSD I can see that these places all have ULSD at the stations on the main highways.
In additoon, using Google Earth, I have located a number of stations randomly picked along main highways leading to Mexico City, used Streetview to look at the Pemex sign, recorded the number and then checked the Pemex list they sent me. Bingo - those stations are on the list, but not the stations a few blocks off the main highway.
This provision was put in place mainly for truckers so that modern delivery trucks, presumably from the USA, are able to access ULSD while in Mexico.
Pemex's information about refineries already converted to produce ULSD is confirmed in new articles in the Oil and Gas Review. The Oil and Gas Review reveals which contracts were let for de-sulfur plants and the timeline. I'll happily post links after I return to Los Barriles in a few days.