Some hooks come as double- or triple-gang hooks, meaning that there are two or three hooks on a single shaft.
How Big A Hook Is Enough? Needle points have good penetration, but not as good as knife edge hooks.
However most hook manufacturers do use the 'standard', but some the one size up convention.
Like and material sizes, fly fishing hook sizes are based on a bit of an antiquated system that doesn't make a lot of sense to us these days.