IMO a poor construct for 'generosity' and 'prosocial'

Run some tests where the high narcissists can give away stuff in a test scenario and nobody will know about it (the test says so - but it lies and records the results) vs regular generous people and see if your construct of 'generosity' holds up. Or whether they aren't generous or prosocial, they are transactional. They are just excellent at fooling researchers and others into thinking they are generous and prosocial.