In de EF they are called Sundays "in" Lent: Dominica I in Quadragesima. In the OF they are called Sundays "of" Lent: Dominica I Quadragesimae.
My takeaway was that Lent originated as a tithe of 365 days, with Ash Wednesday a relatively new-fangled rounding up. Wednesday to Palm Sunday gives 40 days (but not 40 nights?) in the desert. Counting by sixes and skipping alleluialess Sundays, the Triduum starts on day 39. Is this trying to tell me Palm Sunday is 'of' Lent?other discussions of this question on our Forum
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