Indeed, everything on a single ticket (including non-OW) should be protected as this then constitutes one contract from first point of origin to final destination.

By contrast, HappytoHelp was kind enough to tell us in what cases BA goes beyond that to protect successive and separate contracts and it is effectively limited to one very specific case (BA to BA, 125 tix, gap above notional MCT). Of course one might get lucky in other cases (it happens) and equally BA's current policy might change in the future (either for the better or for the worse) but it is great to have that formal pointer in mind even if it is not in writing and if it is possible that contract staff in some outstations might be unaware of that policy.