Okay Paul,
First we need to have an educational session on Collects.
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Collect
The name now used only for short prayers before the Epistle in the Mass, which occur again at Lauds, Terce, Sext, None, and Vespers. The word collecta corresponds to the Greek synaxis. It is a noun, a late form for collectio (so missa for missio, oblata for oblatio, ascensa, in the Gelasian Sacramentary, for ascensio, etc.). The original meaning seems to have been this: it was used for the service held at a certain church on the days when there was a station somewhere else. The people gathered together and became a "collection" at this first church; after certain prayers had been said they went in procession to the station-church. Just before they started the celebrant said a prayer, the oratio ad collectam (ad collectionem populi); the name would then be the same as oratio super populum, a title that still remains in our Missal, in Lent for instance after the Post-Communion. This prayer, the collect, would be repeated at the beginning of the Mass at the station itself (Bona, Rer. liturg., II, 5).
The present rule about the collects is this: on doubles only one collect is said (that of the feast), unless any other feast be commemorated, or the pope or bishop order an oratio imperata. The imperata is, moreover, omitted on doubles of the first class, Palm Sunday, Maundy Thursday, the eves of Christmas, Easter, and Whitsunday, in Requiems, and solemn votive Masses. On doubles of the second class it is left out in high and sung Masses, and may be said at the others or not, at the celebrant's discretion. For a very grave cause an imperata may be ordered to be said always, even on these occasions. It always comes last (De Herdt, I, 72). The collect of the Blessed Sacrament, to be said when it is exposed, and that for the pope or bishop on the anniversary of their election, coronation, or consecration, are particular cases of imperatæ. The rules for commemoration of feasts, octaves, ember days, and ferias of Advent and Lent are given in the rubrics of the Missal (Rubr. Gen., VII; cf. De Herdt, I, 70-71). On semi-doubles, Sundays, and days within an octave, three collects must be said; but on Passion Sunday, on Sundays within an octave and throughout the octaves of Easter and Whitsunday there are only two (Rubr. Gen., IX; De Herdt, I, 75, where the rules for these collects will found). But in these cases the number may be greater, if there are commemorations. On simples, ferias, and in Requiems and (not solemn) votive Masses, the celebrant may also add collects, as he chooses, provided the total number be an uneven one and do not exceed seven (Rubr. Gen., IX, 12; De Herdt, I, 83).
The rule about the uneven numbers, on which the S. Congr. Rit, has insisted several times (2 December, 1684; 2 September, 1741; 30 June, 1896), is a curious one. The limit of seven prevents the Mass from being too long. In any case the collect of the day always comes first. It has Oremus before it and the long conclusion (Per Dominum, etc.). The second collect has a second Oremus, and all that follow are joined together without intermediate ending nor Oremus till the last, which again has the long conclusion. This separates the collect of the day from the others and gives it a special dignity, as a remnant of the old principle that it alone should be said. The conclusions of the collects vary according to their form and references (Rubr. Gen., IX, 17). The people (choir or server answer Amen. During the conclusions the celebrant folds his hands and bows towards the cross at the words Dominum nostrum Jesum Christum. It should be noted that the great majority of the collects are addressed to God the Father (so all the old ones; the common form is to begin: Deus, qui); a few later ones (as on Corpus Christi, for example) are addressed to God the Son, none to the Holy Ghost. At low Mass collects are said aloud so that they can be heard by the people, at high (or sung) Mass they are sung to the festive tone on doubles, semi-doubles, and Sundays. On simples, ferias, and in Masses for the dead, they have the simple ferial tone (entirely on one note, fa). The rules of the tones, with examples, are in the "Cæremoniale Episcoporum" I, xxvii.
Now we can go looking for the answer.