I finally managed to get the OneWorld 100k bonus (8000 points) on Iberia. I did it with the following flights:

BA6406 Cape Town/Johannesburg, operated by Comair
QF3430 London/Amsterdam, operated by BA
IB1240 Barcelona/Málaga, operated by Aviaco
CP6490 Montreal/New York, operated by AA
AA1775 Newark/Chicago

Only one of the flights was really operated by the carrier indicated in the flight code printed on my ticket. The four code shares were counted as the carrier shown on the ticket, not the actual operator. This is apparently fully in accord with OneWorld policy, but it is still difficult to believe. On the Star Alliance it would have been impossible.

I had a good deal of trouble getting these flights credited to Iberia because OneWorld is apparently incapable of registering more than one frequent flyer program per computer record. I also had problems with BA and AA, but in the end it all fell together: for the 100k bonus AA was the easiest, then BA, and, finally, IB. So far, the miles have been pretty easy to use: both AA and IB came up with the flights I wanted, in the class I wanted, on the days I wanted. I haven't tried BA yet. By the way, the IB Plus service desk for the US in Miami was most helpful. I am grateful to IB's Ana Duarte for all of her help!