Datapoint on AeroMexico here ... I have a trip LHR-MEX-LHR on AM and wanted to add my SAS Eurobonus frequent flyer number to the AM booking but was struggling to get it accepted. Similarly trying to enter a Virgin Atalantic FF number. Sometimes it accepted the Virgin number and said it had updated, then showed an error bar and it had not updated at all. This was on the AM website and on both their old and new apps. For SAS it would not accept it at all with or without an EB at the front, with or without a space before the numbers. Then I followed DeathSlam 's post above and entered EBGxxxxxxxxx (as mine is a gold level) and SAS Eurobonus as the programme and hooray, it accepted it on the website. It is now showing on the website and on both apps, although the older app shows the ff program as "_NO-ID-DEFINED_" while the newer app does show "Scandinavian Airlines" as the program. Don't you just love technology. Hopefully this will stick now, and get credited to SAS. I will check the boarding passes carefully when issued.