Changing unit entitlements is difficult and expensive. I’d be surprised if this is what has happened. Areas like private courtyards etc. are generally common property with exclusive use. Sometime however this is not formal if the building is old. It would help to get a map of the building and the boundaries of the lots to help determine how to approach the issue. Most of the time items like these would be owned by the OC like an exterior wall of the apartment etc. as they are external to the lot (unless there is a by-law of course).