Gabriel Fauré wrote three distinct versions of his Requiem, op. 48. The first version of 1888 did not include the Offertoire and the Libera me. The second version of 1893 and the third version of 1900 included all the movements (even though the Libera me had been written already by Fauré as an independent work in 1877). Then, the original manuscript of the second version was lost, and only rediscovered in the early 1980s. Furthermore, the published score of the third version included many misprints and other inaccuracies (Fauré is believed to have delegated the scoring of the third version to an assistant).

As a result of the above historical reasons, today's editions of the Requiem show some differences in the vocal parts. Choralia provides two editions of training aids, so as to best match the score edition used by the choir. Both the editions are derived from the public domain edition #1291 available at CPDL. Then Edition 1 is checked against the edition published by Schirmer (HL 50324670), while Edition 2 is checked against the edition published by Bärenreiter (BA 7513). The vocal parts of the two editions differ for the following details.

Introït et Kyrie

All voices, measure 6: the duration of notes is 4/4 in Edition 1, while in Edition 2 it is 3/4 followed by a 1/4 rest.
Soprano, measure 49: the duration of note D is 1/2 in Edition 1, while it is 3/4 in Edition. 2. The duration of  the rest until the end of the measure changes accordingly.
Alto, measure 51, beat 1-3: there are two A notes (1/4 + 1/2) in Edition 1, while they are F in Edition 2 (duration unchanged).
Tenor, measure 22, beat 3-4: the duration of the two A notes is 3/8 + 1/8 respectively in Edition 1, while their duration is 1/4 + 1/4 in Edition 2.
Tenor, measure 25: in Edition 1 there are two notes, i.e., a 3/4 C (syllable "pe") and a 1/4 C (syllable "tu"). In Edition 2 there are four notes: a 3/8 C (syllable "pe"); a 1/8 C (syllable "tu"); a 1/4 C (syllable "a"); a 1/4 B(b) (syllable "lu").
Tenor, measure 26: in Edition 1 there are four notes, i.e., three consecutive 1/4 A's (syllables "a", "lu", "ce") followed by a 1/4 D (syllable "at"). In Edition 2 there are three notes: a 1/4 A (syllable "ce"); a 1/2 A (syllable "at"); a 1/4 D (continues syllable "at").

Offertoire

No difference.

Sanctus

Soprano, measure 30: the duration of note B(b) is 1/2 in Edition 1, followed by a 1/2 rest, while in Edition 2 it is 3/4 followed by a 1/4 rest.

Agnus Dei

All voices, measure 84, beat 1-3: in Edition 1 the duration of the notes is 3/8 followed by a 1/8 rest, while in Edition 2 it is 1/4 followed by a 1/4 rest.

Libera me

Alto, measures 54 to 56: in Edition 1 all notes F are present, with different duration; such notes are A instead in Edition 2 (duration unchanged).

In Paradisum

Bass, measure 54: the last note in the measure (1/8) is A for B.II in Edition 1, while it is B in Edition 2.
 

 (Source of historical information: Wikipedia)