Pretty much anyone would just add a random quart in there. Your old sump has 1 quart in there and manufacturer reformulate all the time, what do you think is going to happen? It is fine.
I had Valvoline 5w40 in my Xterra. Noticed it was getting low and topped it off with 1QT of Quakerstate 20w50. oil level hasn’t decreased at all since I’ve added it. Valvoline had only been in the sump for a month or 2 at best. Your Caprice won’t mind at all.
Pretty much anyone would just add a random quart in there. Your old sump has 1 quart in there and manufacturer reformulate all the time, what do you think is going to happen? It is fine.