Robert MacGrogan wrote:

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.

I'm not seeing that; the behavior I'm seeing is the behavior that you say is correct. For example, "zdump -Vc 2018,2019 America/Grand_Turk" outputs:

America/Grand_Turk  Sun Mar 11 06:59:59 2018 UT = Sun Mar 11 02:59:59 2018 AST isdst=0 gmtoff=-14400
America/Grand_Turk  Sun Mar 11 07:00:00 2018 UT = Sun Mar 11 03:00:00 2018 EDT isdst=1 gmtoff=-14400
America/Grand_Turk  Sun Nov  4 05:59:59 2018 UT = Sun Nov  4 01:59:59 2018 EDT isdst=1 gmtoff=-14400
America/Grand_Turk  Sun Nov  4 06:00:00 2018 UT = Sun Nov  4 01:00:00 2018 EST isdst=0 gmtoff=-18000