The Eve of the Assumption is a day to say Vespers from any form of the Roman Rite which precedes the post-Conciliar 'reforms'. So as to have the magical experience of actually beginning the Office with that great shout of triumph and joy suddenly going forth: Assumpta est Maria in caelum gaudent Angeli laudantes benedicunt Dominum. Imagine the day of Mary's Transitus and that cry re-echoing ever outwards among the innumerable circles of the oyeresu to the uttermost extremes of the Universe! Compare that with the pedantic Marian minimalism of the Liturgy of the Hours. You can just imagine those grim committee-men sitting round their table ... "We really had better begin the Assumption by setting it in the theological context of the Ascension of Christ". I gather, incidentally, that the Antiphonale offers as the first antiphon at first Vespers Quae est ista, which at least shows a decent liturgical sense still surviving somewhere!
Even the Pius XII forms still have Ave Maris Stella at II Vespers, despite Fr Genovesi's dominance of the rest of the Hymnody. In Pius XII's time they at least kept Ave Maris Stella for II Vespers on most Marian Festivals. The 'reformers' knew better and they knew wrong.
The real loss in 1951 was of the Collect for the Assmption. We beseech thee O Lord forgive the offences of thy servants: that we who are not able to please thee by our own deserts; may by the intercession of the Mother of thy Son our Lord be saved. (Happily, it survives as an optional collect for our Lady in the Liturgia Horarum.) It was replaced by a modern composition which I must confess to finding inferior to the older one. The older collect emphasises the ancient conviction of East and West that the purpose of the Assumption is that our Lady might intercede for us; it reminds us that only through the Mediatrix of All Graces, reigning body and soul in heavenly glory, can we attain Salvation; it always reminds me of the homilies of the Greek Fathers, culminating in S Gregory Palamas, about the Mediation of our Lady. And of the plea one hears in the Byzantine Rite Most Holy Mother of God, save us.
Indeed ... soson hemas ...