I’ve been determined to finally beat Zelda II and determine that I would do it without save states and without a guide.
I know Zelda II is considered a black sheep somewhat but I really think in some ways it’s more fun than the original although I’d still pick Zelda 1 over II.
I would be careful with the word "always". A softlock can occur by entering a later dungeon to steal some of its keys. You can use the surplus keys to beat an early dungeon without collecting its item. This locks the item in the dungeon. Hope you didn't need that later.
But couldn't you go to where the alternative dungeon's keys are, get those and come back to get the earlier dungeon's item that way?
I can't see how you can softlock?
It seems I was wrong in that you can't lock an item in a dungeon by beating it. But you can lose keys to a dungeon turning it into a mountain with keys inside. So using a later dungeon's key to skip a key could softlock you.