Holy Week was included in the 1962 missal and is binding/law, being a lawful revision of Quo Primum. The 1969 missal is neither binding nor lawful, being at odds with Quo Primum and also, secondarily, the 1969 law does not command anyone attend/say the new mass. But all this has been discussed before...
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The true question is, why does a sede think that Pius XII wasn't the pope? Or why didn't he have the authority to slightly change Holy Week?