The question assumes that accuracy and realism were the end goal of the artist or the subject, or at least would be a desirable outcome. I'm not sure that's a fair assumption. We live in a world influenced by photography. Portraiture can imitate photography because photography exists to imitate. Prior to that development, capturing the "essence" or displaying the beauty of a subject may have been more desirable.

Let's say you're painting a portrait of Washington. The man was known to be stern, but fair. He was generous to friends and supporters but also had a fierce temper if pushed too far. He carried himself with the surety and sense of nobility that a planter from a FFV would have. But those aren't physical characteristics. Still, the artist would be expected to convey those qualities through their work. So maybe you broaden his shoulders, soften his eyebrows to emphasize his eyes, reduce the swelling in his jaw, get rid of a few wrinkles in his brown, straighten his nose to be more reminiscent of Roman emperors (Idk if that was actually done except for the jaw thing. Just examples). You convey the essence of the man and not just his image.