I can only find reference to one type 42 destroyer, have you got a link.
But here's the thing, we weren't at war with them at the time of the sale. The French were out there helping with testing equipment whilst the conflict was on.
Which at the time was being superceded by the Super Etendard, until the EEC embargo kicked in.
Argentina's fleet of A-4 Skyhawk attack jets was in very poor condition. The arms embargo placed by the United States in 1976, due to the "Dirty War", had made most airframes unusable. The involvement of Israel in helping to return the A-4 to full operational status has been alleged, but has never been confirmed.[12]
International arms trade is a dirty business and we "UK" are a major player, you might have missed the irony of HMS Sheffield and ARA Hercules, worth a look