It looks to me like the time zone data for America/Grand_Turk is incorrect in 2018e version of the database. Turks and Caicos switched to supporting daylight savings time in March of 2018. So in summer the correct time for America/Ground_Turk should be GMT -4 and then back to GMT -5 again in the fall.
The current database returns times for summer of 2018 as GMT -5, which is incorrect.
