The Reform mandated by the Council of Trent was not something achieved overnight. It took virtually fifty years under several popes and the 'Sacred Congregation of Rites' (set up in 1587) to see the whole gamut of liturgical practices revised and restored according to the principles of the Fathers of the early Church. The primary objective of Trent was not to produce a Tridentine Rite as such, but to offer the Roman Rite with its range of liturgical books in a format that did not exclude the local customs and calendars of dioceses and religious orders, which could prove that their books were over two hundred years old. In the legal tradition of that time, a 'custom' in law was defined as something a hundred years old. It was therefore deemed as valid being less likely to be tainted by the protestant reformers.
Pastoral Liturgy is published by the University of Notre Dame, School of Philosophy and Theology, Fremantle.
Hardiman, R. (2007). The books of the Roman Rite: From Trent to Vatican II. Pastoral Liturgy, 37(1), 9-14.