Since learning how to heart refresh glitch to reach the room beneath the castle gate, I've always wondered why 200.6 was considered complete. Is there some way to reach the room legitimately that I don't know about? The save point down there even seems kind of glitch-y so I really don't think you were intended to reach it. Meanwhile, there are achievements in modern ports of the game for getting 200.6%.
So yeah, heart refresh glitch. Or there's the Sword Bros. glitch to go out of bounds around the chapel towers; I feel like if it's accepted that you need to go out of bounds for sake of completion for the first, why not for the second? You're more likely to have the Sword Bros spell + the bat transformation you need for this one. It'll still get you the achievement regardless of getting the "correct" 200.6%. You can get substantially more defense from Walk Armor just by going outside the chapel towers in both castles. IIRC there's a myriad of other ways to get out of bounds for a few more percent but I never did any others so have no real opinion on them.