The creation date of issues should be set to the blame/scm date, if the issue is raised by a rule, that has been newly activated for this analysis.
The decision table looks like this:
|SCM available?||rule activation date after last analysis date?||resulting issue creation date|
|yes||yes||MIN(SCM blame, analysis date)|
On the first analysis of a project, all rules will be counted as "new".
In the UI, the graph, that shows the technical debt over time, will still face up. Quality gates, that are related to the "total number of issue" will not be affected by this change.