Here is the current GIRM wording from the UK Missal:
63. When there is only one reading before the Gospel:
a) during a time of year when the Alleluia is prescribed, either an Alleluia Psalm or the Responsorial Psalm followed by the Alleluia with its verse may be used;
b) during a time of year when the Alleluia is not foreseen, either the Psalm and the Verse before the Gospel or the Psalm alone may be used;
c) the Alleluia or the Verse before the Gospel, if not sung, may be omitted.
This is the provision for weekdays only ("when there is only one reading before the Gospel"), and is a significant modification of what was previously in GIRM which provided more options.
The possible omission of the Gospel Acclamation if not sung was originally (in 1969 GIRM) the case on Sundays as well as weekdays, but this was subsequently changed in the 1981 edition of the Lectionary (
The Alleluia or the verse before the gospel must be sung and during it all stand — if it
must be sung, then presumably it can never be omitted). GIRM para 62 now replicates some of what is in GILM (1981) 23.
62. After the reading that immediately precedes the Gospel, the Alleluia or another chant laid down by the rubrics is sung, as the liturgical time requires. An acclamation of this kind constitutes a rite or act in itself, by which the gathering of the faithful welcomes and greets the Lord who is about to speak to them in the Gospel and profess their faith by means of the chant. It is sung by everybody, standing, and is led by the choir or a cantor, being repeated as the case requires. The verse, on the other hand, is sung either by the choir or by a cantor.
23. The Alleluia or, as the liturgical season requires, the verse before the gospel, is also a ‘rite or act standing by itself.’ It serves as the assembled faithful’s greeting of welcome to the Lord who is about to speak to them and as an expression of their faith through song.
The Alleluia or the verse before the gospel must be sung and during it all stand. It is not to be sung only by the cantor who intones it or by the choir, but by the whole congregation together.
GIRM 62b is also relevant to weekdays during Lent as well as Sundays:
b) During Lent, instead of the Alleluia, the Verse before the Gospel as given in the Lectionary is sung. It is also possible to sing another Psalm or Tract, as found in the Graduale.
Unfortunately confusion often arises in the minds of parish musicians because of the terminology used.
"Alleluia" means the entire Acclamation: Triple Alleluia, scripture verse, Triple Alleluia.
"Verse before the Gospel" does not mean the scripture verse but the entire Acclamation during Lent: "Verse" (e.g. "Praise to you, O Christ, king of eternal glory"), scripture verse, "Verse". In other words, the Lenten Verse before the Gospel includes a scripture verse within it, just like the Alleluia does.
Because of the likelihood of confusing "Verse before the Gospel" with the scripture verse, it would have been much better if they had used the word "Acclamation" for what happens during Lent.
Acclamatio ante Evangelium would have been less confusing than the present
Versus ante Evangelium.
I don't see the omission of the Alleluia or Acclamation as a recommendation, merely a possibility ("may be omitted").