Importance of knowing the person for portrait painting

I just finished a commissioned portrait painting  (not the one pictured here ) from a photo . I didn’t know the person so wasn’t familiar of what he really looks like so wasn’t able to be a good judge on whether my painting done was a good likeness of him.  I find it important to be able to know and be aware of what the person looks like on top of your head before doing the portrait painting, which is why prominent portrait painters even Sargent often set up meeting with their sitters and studied them in person to get to know them before starting the final portrait painting .They’d do this even when they’d work from photo references. In person meeting is most efficient and fastest way to get to know what the person looks like when you don’t know them, but it can be done also through many photos and videos, which I didn’t have access to. But If it was a famous person such as Tom Hanks for example, I’d know what he looks like so I’d be able to judge well on the likeness of a painting I’ve done of him from a photo