It's been awhile since I checked the available full installers for High Sierra. Haven't seen this 17G66 build version before. Has anyone used the 17G66 installer for High Sierra 10.13.6 on MP5,1's? Cannot find documented info on this forum or any Wiki posts. 17G2208 believe was just for 2018 MacBook Pro's 17G65 was widely installed by many and well documented 17G5019 is latest available update for most MP5,1's All packages in the 17G66 installer are dated December 14, 2018.