The six initial -500s received by BA failed to meet their performance guarantees, allegedly by nearly 10%. In consequence they were returned to Lockheed for retrofit of the extended wingtips and active ailerons and the lower sfc -524D which became standard production features. Even so, they could not operate LHR-LAX without a payload penalty.
The six (6) BA -500's along with two (2) Delta and one (1) BWIA -500's were delivered with the standard -1 wings (sans active controls). There was no performence guarantees applied to these aircraft as all the operators knew they were not the baseline configuration. Once the active controls flight testing was completed, using the house aircraft s/n 1001 and two Pan Am -500's, all nine (9) of the -500 with the short wings had the wing extensions retrofitted along with the active controls.
An interesting fact: With-in a year of BA selling their -500's to the RAF they turned around a leased the two (2) Air Lanka -500's and operated them or three (3) years.