It is a painting made by an artist relying on eye witness accounts, at best, and having never actually seen the subject they are painting.
So missing details is not only understandable, but make sense if you view this as painting made in setting.
I watched couple videos by a smith who makes historical replicas and movie props of medieval weapons (and other stuff), and they made a very good point about how perfection is inauthentic, because most things are not, especially so things made with technology available in pre modern times, where what we would consider high quality would provide fairly minor benefit, for a huge cost in time to make.