"BA might have O class fare LOS-LAX or LOS-CPH. Irrelevant if no O class fare basis LOS-LHR."
That's not correct, there are many instances where a cheaper fare is filed to a distant destination than is filed to a closer point that is a stopover on the longer journey. This is what is exploited with hidden city ticketing.
For the rest, you have a point. As well as no fares for the cheapest selling classes, there also seems to be a lack of availability in any class less than Y for a Nigerian point of sale (such as a straightforward Nigerian travel agent).