a bookmark:
Playing with Project Templates for VS 2017 ...
templates are Zipped by Visual Studio ... saves in 2 places
in ProjectTemplates used by VS
and a backup in My Exported Templates
I had some templates that continued to show in the project startup dialog after they had been deleted from the default locations.
I tracked the cached location to
C:\Users\kdub_\AppData\Roaming\Microsoft\VisualStudio\15.0_dc662b10\ProjectTemplatesCache\ ....
Deleting the cached zips has fixed the issue.