But the Argentinean claim was never based on our 18th century claim having lapsed, so they're not being hypocritical in refusing to take account of their failure to press their claim for many years. They didn't recognise our claim as having any validity in the first place. To them (& here, they have a good point), our settlement in 1766 didn't give us any rights, as there was already a French settlement & a live Spanish claim, & the French ceded their claim & settlement to Spain.
There are actually a couple of problems here which can muddle this even further.
While the Spanish did indeed attack and expel the British garrison at Port Egmont in 1770, following an agreement signed in London in early 1771 between Britain and Spain, British possession of the port and garrison at Egmont was restored. Further, the agreement left intact both British and Spanish claims to the islands.
Muddling the issue further still is the Nootka Sound Convention/Treaty of San Lorenzo of 1790, specifically the Secret Article ratified Nov. 22nd
SECRET ARTICLE said:
Since by article 6 of the present convention it has been stipulated, respecting the eastern and western coasts of South America, that the respective subjects shall not in the future form any establishment on the parts of these coasts situated to the south of the parts of the said coasts actually occupied by Spain, it is agreed and declared by the present article that this stipulation shall remain in force only so long as no establishment shall have been formed by the subjects of any other power on the coasts in question. This secret article shall have the same force as if it were inserted in the convention.
Given that this convention was between Spain and Britain, once Argentina (another power) attempted to establish itself on the Falklands, the British were no longer obligated to not form an establishment on the Falklands either.
Yet more potential for confusion.
Buenos Aires which is now the capital of Argentina was the capital of the Viceroyalty of the Río de la Plata, up until 1810 and the May Revolution. At which point Buenos Aires effectively ceased to be part of the viceroyalty and became self-governing, even though a formal declaration of independence was not made until 1816. Following the May Revolution, the capital of the viceroyalty was transferred to Montevideo which is now the capital of Uruguay and Montevideo remained the capital of the viceroyalty until it effectivel ceased to exist following the defeat of Spanish forces in Montevideo in 1814. Part of the reason this is important to note is because a Spanish garrison and later penal colony was maintained at Port Louis until 1811, at which point the Spanish garrison was evacuated to Montevideo. The result of this is that Uruguay, or indeed any of the other nations that had land that had once been part of the Viceroyalty of the Río de la Plata could claim status as an 'heir of Spain'. Going yet further with this, Spain contested the independence of the various South American nations up until the mid-1820's. Spain apparently does not end its legal claims to Argentina until treaties signed in 1858 and 1863.
What makes this particularly interesting is that the treaty of 1863 has Spain recognizing the following:
Article 1: said:
Your Catholic Majesty recognises the Republic or Confederation of Argentina as a free, supreme and independent nation that consists of all the provinces mentioned in its present federal Constitution, and other legitimate territories that belong or could belong in the future.
At the point at which Spain renounced its claims to Argentina, a British colony on existed on the Falklands for a generation...
Making things stranger still, Louis Vernet, the Argentinian who initiated a failed colonization attempt in 1824 and then again in 1826, sought a land grant from the British Consulate in Buenos Aires in 1828 for the land on the Falklands.
Then of course there is the 1850 Convention of Settlement, where diplomatic relations were resumed between Britain and Argentina. Britain at this point had been in possession of the Falklands for ~16 years and no mention was made of any claims by Argentina for them.
The 1870's were from an international diplomacy POV a noteworthy time for the Falklands, with the US, Chile, Sweden/Norway, Belgium and Germany opening consulates in Stanley.
In 1882 there was also something of significance. The Argentine Foreign Ministry financed a map now known as the Latzina Map of which ~120,000 copies were made. The reason this is significant is that the map has the territory of Argentina marked in one particular colour, and also shows some terrain features. Non-Argentinian territory was marked in another colour and did not show terrain features. On the map, the Islas Malvinas as they are marked, and Chilean territory are coloured the same, i.e. they are both non-Argentinian. This difference in land mass colouration indicating the territory being outside of Argentina is apparently what led arbitration judges at the ICJ in 1977 to rule that 3 Beagle Channel islands belonged to Chile and not Argentina.
That is it from me for now.
-Cheers