After a while, when a new bug found, most likely,

* Adding one or several test step (in existing test cases)

* Update existing test script

Not adding each newly found defect as a new test case, that will be duplication. Test maintenance is the key. If the team maintain the test suite well, they will know test scripts well, so, mostly will be just updating existing test script. In this case, it can be considered "adding", as the old test script new check for more scenarios.