I was referring to the construction of the breakers... two individual breakers being side by side mechanically connected with a handle tie for common trip. if you removed the handle tie, and connected single branch circuits to each, then they would act as individual breakers. but the OP is discussing QO style breakers which are 2 pole breakers with one handle. you can't separate that into two individual circuits. I regret making the case.
I understand what you are saying.
But,
Even though the the (2) Separate breakers are "joined" together physically they do not act as "Individual" breakers.
On a 2p common trip even without the handle tie, if one side trips, both sides trip, but, one side cannot be reset without the other side being reset.
Both sides have to be reset at that same time as if the handle tie was still in place.
Therefore they actually do not function as (2) individual breakers.
If they were actually (2) individual breakers simply "joined" together, and, you removed the handle tie, one would not trip when the other one did, and, one would not be dependent on the other to reset like an actual 2p common trip breaker is.
JAP>