Bluehouse – no you’re not being terribly pedantic (that’s usually my role 
), but I think that you may be placing too much emphasis on what’s shown on the Strata Title Plan in the context of seeking your Owners Corporation’s consent to planned renovations to your Lot.
Common areas of a Lot are by definition those that are shared with other Owners and with the Owners Corporation as if those were separate entities, and using my shoe box analogy that’s the perimeter sides, the bottom, and the lid.
So anything that you may wish to do that could involve any of those areas needs to be discussed with, and in the case of Strata logically consented to by the Owners Corporation irrespective of what’s shown by the thickness or design of lines on a Plan.
Remember also that renovations to a Lot may not just involve areas in common with others, but may also involve internal load bearing walls, environmental impacts such as vibration and noise, and related impacts such as the movement of contractors and their equipment / vehicles around the property.
All the more reason why you and other Owners should simply provide details of whatever renovations may be proposed to your Executive Committee, and let them liaise with others including your Owners Corporation as a whole and facilitate the appropriate consent and any conditions.
In the context of renovations anyway, don’t get to hung-up on interpreting the Strata Title Plan.