...

In any other case, the violation is a new one.

Info

title	I am not getting the expected new violations in the Violations drilldown service when a differential view is selected?

Three reasons can explain this:

This Violations drilldown service only shows added violations, not fixed ones. Therefore the number you see in this service can be different from the one displayed on a dashboard through the Rules Compliance widget (that displays added violations - fixed violations).
The algorithm detecting new violations is very good but still perfectible. Therefore new violations can sometimes appear only because Sonar did not recognize it already existed.
You are looking at a period of X days which goes beyond the first analysis made after migration to Sonar 2.5. In this case there can be a discrepancy due to the fact that prior to 2.5, Sonar was not collecting the info necessary to build this service. This issue will disappear as soon as period does not go beyond first analysis.

Code Coverage on New/Changed Code

When activating the SCM Activity Plugin, you will be able to separate coverage by unit tests of new code from old (based upon a given cut-off date) in order to track the new code which does not have any/enough unit tests.

Git