About switch 2 upgrade packs for Switch 1 games

Are these upgrade packs tied to an account? Meaning do the upgrade packs only work on the account that purchased them? Can you share them with a family member who is linked? My situation is my girlfriend has a switch 1, I have a switch 2, my niece has a switch 2 now also. If I buy a game on switch 2 only I or my neice can play it on our respective switch 2 consoles. If I buy a switch 1 game I can let my girlfriend play it if I give her access to the virtual game card or just give her the physical card to use in her console. However what I'm wondering is if I buy a game for the switch 1 then purchase an upgrade pack, does my neice have access to the upgrade pack as well when she is borrowing the game or does she need her own upgrade pack? It would be nice if I could buy a game for switch 1 and then the upgrade so everyone could borrow it sometime but if my neice wouldn't get the upgrade then I would just buy the switch 2 version of the title all at once.