Are boss upgrade drops missable?

I've never played PoE 1, so I don't know if this is common, but I feel like Act boss upgrades (such as weapon skill points, spirit, or resistance buffs) shouldn't be a consumable item that you pick up. Is it missable if you don't grab it? I know there's a button to turn off the UI that automatically shows loot drops.

I was unaware that bosses drop consumable items that give skill points and resistances until I started researching PoE 2. I'm assuming I grabbed everything from Act 1 bosses (I cleared all the maps my first time through). But that's another problem; there's no intuitive way of knowing that I got these boss drops by hovering over the skulls on the map. I know it's grayed out if I've defeated the boss, but that's it.

Does this also apply to story-based loot caches and quest rewards? I wish there were a UI tracker that showed whether you missed one of these, or better yet, it shows up in your stash or inventory if you somehow weren't able to pick it up or didn't even notice that one of these items was used as a passive, permanent buff.

I like how Last Epoch does it, where the map shows what passive buffs and item slots are left to unlock in that Act, and it happens without having to collect consumable items per Act.