The recipient names in the letters of Isidore of Pelusium have a different textual history to the body of the text. These names appear at the top of each letter, sometimes followed by a one-line summary.
I learn from Pierre Evieux’s excellent study that in the manuscripts, these items were not copied at the same time as the rest of the text. This is because they are written in red, and are therefore done by a rubricator. The copyist had to leave a space for them, and then someone — himself or another — would come back and fill in the gaps in red ink.
The same approach was taken in medieval texts to decorated initials. Quite a large number of those initials were never done, and there are many manuscripts which still have a gap at the appropriate place. So we can see immediately that the names can be lost in transmission far more easily than the rest of the text.
Nor is this all. In a modern edition the names would be on a separate line. But in a manuscript, saving parchment is all — especially if you had to kill the sheep necessary to make that parchment! So the names would be inline, and distinguished by the colour to indicate the start of a new letter. If you didn’t leave enough space, what then?
The only possible answer would be to abbreviate the words. But names are hard to abbreviate. Consequently the result could well be obscure symbols, also leading to loss. This would be hard to fix next time the text was copied, especially as the next copyist would be liable to leave the same amount of space, thereby preventing the abbreviation from being expanded.
Finally the red ink tended to fade more than the black ink, leaving portions illegible. A few scattered letters would be all that could be copied.
A further factor is the nature of the manuscript. When it contained a copy of the letters of Isidore of Pelusium, the names of the recipients were important to the reader, and are generally included. But there are also manuscripts which only contain a selection by subject of his letters, e.g. on some point of scripture. In these manuscripts the name of the author was important, as an indicator of authority, but the recipient names hardly so. In these type of manuscripts the recipient names suffer much more damage.
All these features are found in the manuscripts.
These interesting comments by Pierre Evieux would seem to have wide application to many other sorts of texts. They explain how letters can easily be combined in transmission; how the names can easily be corrupted or mistaken. All these little details help us to understand what we see in any text that has reached us.