Corrections
The scribe or scribes responsible for producing Western Ms 097 often noticed the mistakes in the text and attempted to fix them.
Mistakes are most commonly corrected with a line drawn through the erroneous text. These lines can be either brown or red, suggesting that there were multiple scribes involved in checking and revising the manuscript. Alternately, the corrections may have been performed by the same scribe at different points in the writing process, depending on when the mistakes were noticed.
This corrector-scribe used brown ink to correct the third-person singular "faciet" to the third-person plural "faciunt." Whether this corrector was the same scribe who wrote the main text and/or the musical notation, or a different person altogether, is hard to say--though the hand looks considerably sloppier than that of the main text.
Here, the strikethrough has been done in red. This could have been the same scribe who was reponsible for the red initial, or the rubric indicating the chant is to be sung at communion, or both. He or she must have noticed that "uocem mea" should be "uoce mea."
Usually, when the mistake is orthographic, the the accurate text is then written above the correction.
The scribe originally forgot the "ri" in "misericordiam," so it has been added in above the text. Note that the syllable is closely aligned with the musical note it was presumably meant to be sung on.
The text here should read "ab alienis" - the a has been indicated over the text in the staff, and the corrector has added a separating line between "ab" and "lienis" to ensure the reader is aware of the correction. Corrections have also been made to the musical notation.
At other times, the crossed-out letters are simply rewritten elsewhere in the space of the main text. In these instances, which are quite common throughout the manuscript, the error seems to have occurred in the alignment of the text with the musical notation; the correction would have ensured that the right syllables were sung with the right intonations.
The "om" in "omnes" was originally written later along the line, but a scribe has crossed it out in brown ink and rewritten it so that it aligns with the earlier notes.
The last syllable of "peccatorum" is similarly stricken through in brown and rewritten under notes that, without the correction, the manuscript's readers would have sang on the previous syllable "tor."
The "per" in "pauper" has been written twice: both in brown ink, although the slightly different shades and hands suggest that either two different scribes, one writer and one corrector, used brown ink. Perhaps the corrector scribe, who wrote with the lighter brown ink, was the same scribe responsible for the musical notation, as the shades are similar. Either way, spatial corrections such as this indicate the importance that the users of this manuscript placed not only on the textual accuracy of the liturgy but on the relationship between the text and the musical content.
Strikethroughs are not the only form of correction appearing in the manuscript, however.
Here, the scribe has attempted to write the proper letter forms on top of the mistaken ones, so that "iustiaicaciones" is corrected to "iustificaciones."
Sometimes, the original ink has left an impression showing what was there before the correction, such as here in which the second syllable in "ego" was written too far along the line, erased, and rewritten to align with the correct musical notes.
These kinds of corrections, however, are somewhat rare. More commonly, when erasure has occurred, it is more thorough. In these latter instances, the texture of the parchment is usually coarser than that of the rest of the page, suggesting that the mistake has been scraped off of the surface with a knife.
This final syllable of "humiliabam" was clearly written as "bat" at first, until the "t" was scraped off and an abbreviation mark indicating the "m" was added above.
The rough texture of this "o" in "ieiunio" suggests that something else was originally written underneath it, but if so, it has been scraped out too thoroughly to discern what the error might have been.