What happens when a seed contains a locked item?

Say I found a seed which contains an item I just unlocked, right in the first item room. What happens when a new player, who hasn't unlocked that item, plays my seed? I would guess one of the following situations would happen:

1. The 'locked' item will be substituted by an item that isn't locked for the new player;
2. All the items in the seed will be different, because the new player has a different item pool;
3. The entire run will be different, including the rooms and such (RNG will derail);
4. Nothing is different, the new player can obtain the item that is actually still locked.

Has someone tested which of these cases happens?

The item you have not unlocked will be replaced by a random item that you have unlocked. (Your option 1.)