Extraordinary to hear that anyone thinks the Spanish "bequeathed" the Falklands - as they never owned them in the first place!
Neither did Argentina, at any time in the distant past, make a territorial claim to the Islands.
Britain undoubtably made the first documented landing and (much later) filed the first territorial claim as is universally agreed by historians some hundred years before anywhere called Argentina even existed. In any case France had established an outpost there at much the same time as we did and before the Spanish so if mere 'first footing' were to be the deciding factor France has a better claim to them than Spain. The fact that Argentina may or may not have subsequently used the place as a dumping ground for convicts (while failing to file or publish a claim of ownership) gives them no right to any sort of title, as is universally rcognised by international law.