Isn't Ostrom just saying that with effective regulations informed by local knowledge, it is possible for shared resources to be successfully managed?
The "tragedy of the commons" is just what happens in the absence of effective rules governing the use of a resource when individuals are free to act in their own interests.
I grew up near a place that still had a common, the list of bylaws was massive. I think it was >40 and was prominently displayed on the entrance.
The thing is, like most commons, the land was maybe not directly owned, but there was a management responsibility. as in it was owned by the crown but was granted for the use of the towns folk so long as Harry Big Cheese to hunt thrice a year at some obscure feast day.
the point was, management was there, and enforced. Any common that didn't have effective management would fall foul of its rights and legal action would be taken. Or riots.
Common land is owned, but there are group rights.