Consider following git log from branch-1 :
The commit Readme has been created after the latest commit on branch-1. And in org.sonar.scanner.repository.ForkDateSupplier#get we detect of a fork point date between master and branch-1
Thu Nov 25 12:04:45 2021 +0100 . We will use this date later to find all the issues that were introduced on branch-1. But some of the issues were already introduced on this branch before this date (commit bug on branch-1). These issues will not be included in the New Code but they should have been - they are in the end introduced in branch-1 and they are not merged yet to master branch.
This only applies when we use reference branch New Code policy.