The 'historicising' post-Conciliar Revisers reached September 1. Here they found S Giles; he had no proper collect and so he was observed with the Common collect: 'O Lord, may the intercession of blessed Giles thine abbot commend us: that, what we cannot by our own merits, we may attain by his patronage'. Observing that his Vita is fabulosa, they left him 'for particular calendars'. The same day a commemoration had to be made of the Twelve Brethren Martyrs. The Revisers, noting that the Acta of these martyrs were - again - fabulosa and that in any case the twelve were not brothers and that they died in different places, exultantly cried 'deletur!', and so deprived us of the lovely prayer (lovely in the Latin: this is again a merely schoolmasterly translation) 'O Lord, may the brotherly crown of thy martyrs bring us joy: and may it grant us increases in the virtues of our faith and console us with their multiple suffrage'.
So a day which for so long had enabled Christians to express both their diachronic fellowship with the saints of long ago (but who are still our joyful friends in Christ) and their synchronic identity with those in the lands where these saints bore witness, was emptied into feriality ... if you see what I mean.
Legally, however, users of the modern Roman Rite may, on such a 'free' feria, say Mass of any saint ascribed to that day in the martyrology. So Giles or the Twelve could have been observed; but not both together, and not with their ancient collects.