This is the first date-time when the value set version becomes active, so this value is present on Inactive value set versions as well. The start Date_time is expected to be as of 0001 UTC of the Effective Date.
Project FHIR API
This is the location where you can find your resource using a FHIR client.
Simplifier FHIR API
The global endpoint is where users can search for all resources in Simplifier. Resources have a globally unique guid Id here.