I’m not sure there is an expiration date. Wikipedia (so pinch of salt) has the text as reading that Spain ceded to Great Britain: “the full and entire propriet

I’m not sure there is an expiration date. Wikipedia (so pinch of salt) has the text as reading that Spain ceded to Great Britain: “the full and entire propriety of the town and castle of Gibraltar, together with the port, fortifications, and forts thereunto belonging ... for ever, without any exception or impediment whatsoever.”