hlritter

Actually, it's "annus mirabilis" when it's just used to refer to a year of miracles in the nominative case, as "That was my annus mirabilis." "Anno" is commonly seen, but it's usually a mistake. It's the dative or ablative case of "annus", and would be rendered typically as to or in the or a year. So in your original reference, where you did say "in that anno mirable [sic]...", you did have the anno right, if not the mirabilis.