As I told in a previous post, Coventrys´ Sea Dart were launched on 9th may against Learjets not against Skyhawks and all missed. Three missiles were detected and avoided by the argentineans decoy Learjets.
Lt Casco and Lt Farias A-4Cs Skyhawks were lost in bad weather the same day on Jason islands. There is even a letter from 1st Lt Vázquez, later killed on 30th may, in which describes the impossible conditions to fly that morning cause he also flew another flight that had to abort after reaching West Falkland. It´s suposed that they could crash in the air, falling one to land and the other to sea. Both planes carried one solitary Mk-17 1000 pound bomb, so the bomb may be from them.
About debris field in Steeple Jason island, I have some reports on argentine planes that aborted missions and threw his bombs, as a practice, over the islands they found on their way home. I remember one mission on 29th may in which two Daggers (1st Lt Román and Lt Aguirre), after aborting for a CAP presence jettisonned his bombs on islas Salvajes (in english Grand Jason and Steeple Jason islands).
Regards
PD: Don´t know if the fuses were french but the bombs used that day were Mk-17 (A-4 B from FAA) and Mk-82 (A-4Q from Navy)