Hmm, I would have said F-15 would be what you called something that was almost VF-20 lol... or if uncertain of the grade sold it as as Fine/Very Fine.
If Andy Jackson hadn't jostled that change jar holding this coin on Cinco de Mayo in 1832, then it would be a 20. But we all know Andy couldn't hold his liquor, so we're stuck with the F-19.
Yes it's rarely used, but when a sensitive coin such as the 1828 Bust Half is trying it's best to be a VF-20 but is just a tiny bit short you gotta give it the F-19 to let it know that you think it's really a great coin even if it's not a very fine. Trust me, once those Bust Half's start crying there's no stopping them.