Storing data per player without modifying player data

What I'm looking to do is store a list of tags given to the player when they unlock something so that when they die it can then be locked in the order they unlocked them in. One at a time. But I'm having difficulty doing this since you can't modify player data and I'd rather not summon entities if possible as that can be, to my understanding, quite inefficient. Is there a way to create lists of data that are unique to each player, because the only way I can think to do this type of thing is if I use a storage type with data on it but I'm unsure if I can scale that to more than one player.