Indeed, those are the oneworld lounge rules.

IMO the spirit of those rules from BA's perspective are that they can deny entry to someone who is on a flight marketed by another oneworld airline but operated by someone outside the alliance (e.g. hypothetically an AA codeshare with TK or QF codeshare with AF).

It just seems odd that BA would use those rules to deny access to a BA lounge for a flight marketed and sold by BA (on an IB codeshare on Vueling metal). In that scenario any GCH or SCH who is not versed in the fine print of the oneworld rules could be forgiven for imagining that a flight they booked on ba.com would entitle them to BA lounge access.

In other similar cases (e.g. a BA ticket on BE or EI metal or - when it existed - a BA ticket on Meridiana metal), am I right in saying that GCH/SCH would have access to a lounge? Are there any other scenarios where a booking on ba.com results in denial of lounge access for GCH/SCH?

Not complaining; just interested.