I've noticed two more dates in Austen's 'History':
'She was executed in the Great Hall at Fortheringay Castle (sacred Place!) on Wednesday the 8th of February--1586--to the everlasting Reproach of Elizabeth, her Ministers, and of England in general.'
'It is sufficient to say that he was beheaded on the 25th of February, after having been Lord Leuitenant of Ireland, after having clapped his hand on his sword, and after performing many other services to his Country.'