Question re-phrased

In the old days, there was not a real concern if the texts being sung matched perfectly the ones the priest prayed. Deference was made to the traditional version that had been sung for many centuries.

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As proof of this, I have noticed that the 1962 Editio Vaticana Latin Propers (like we find in the Liber Usualis, e.g.) do not always match the Missal texts the priest reads.

For example, in the TRACT for the 1st Sunday of Lent, the 1962 Missal says:

Dicet Domino: Susceptor meus es tu, et refugium meum: Deus meus, sperabo in eum.

However, the chants in the Editio Vaticana read:

Dicet Domino: Susceptor meus es, et refugium meum: Deus meus, sperabo in eum.

I am told that it has always been allowed to simply sing what is in the Editio Vaticana books, even when they are slightly different from what the priest reads at the Altar.

My question is as follows:

When did this rule change? For example, most people say that is not allowed to use Ted Marier's versions of the Responsorial Psalms because they don't use the most current translation. Is this a fact?

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(I also remember reading somewhere that, once a text a is approved for the Liturgy, it can always be used, even when [for example] they update the Lectionary. I was shocked to read this. Anyone else ever read this?)