There is a controvertial point that arose in another entry about a work in the Motu Proprio Summorum Pontificum. The Latin of Art. 5, § 1 says:
In paroeciis, ubi coetus fidelium traditioni liturgicae antecedenti adhaerentium continenter exsistit, parochus eorum petitiones ad celebrandam sanctam Missam iuxta ritum Missalis Romani anno 1962 editi, libenter suscipiat.
This is how I translated it:
In parishes, where there is continuously present a group of the faithful attached to the previous liturgical tradition, let the pastor willingly receive their petitions that Mass be celebrated according to the Rite of the Missale Romanum issued in 1962.
Actually there are a lot of controversial words here…. coetus… adhaerentium… continenter. Another word to examine is exsistit from existo.
Some people have been saying the force of exsistit is that a group of people (leave aside the size) must have already been in a parish for a while.
The problem with this position is that exsistit is present (contemporary) tense and thus refers to right now or the future (because the document will also be read in the future).
But the real fun comes when you consider that, according to the mighty The Lewis & Short Latin Dictionary exsisto only in its secondary meaning means "to be visible or manifest in any manner, to exist, to be".
In its first, or primary meaning exsisto means, generally, "to step out or forth, to come forth, emerge, appear", and in greater precision, "with the accessory notion of originating, to spring, proceed, arise, become".
So, the Latin of article 5, § 1 says equally well:
In parishes, where in a continuous way a group of the faithful attached to the previous liturgical tradition manifests itself, let the pastor willingly receive their petitions that Mass be celebrated according to the Rite of the Missale Romanum issued in 1962.
The force of this is that the provisions of this article of the Motu Proprio apply to what the priest ought to do even when a new group forms, now or in the future. Exsistit indicates its existence now, its continued existence in the future, and its new existence in the future.
What it does NOT refer to is any need that it existed in the past.