A lot of work has been done on mistakes in medieval manuscripts. The main types of copying mistakes are:
- dittography - accidentally repeating a letter, a group of letters, or whole words.
- haplography - accidentally omitting a letter, group of letters, or whole words, particularly when the letters or the words are similar, e.g. "philogy" for "philology".
- homoeoteleuton - this means "same ending" and it is when a scribe's eyes jump to words with the same ending and inadvertently miss out a few words or even a few lines.
- homoeoarchy - this means "same beginning" and it is when a scribe's eyes jump to words with the same beginning and inadvertently miss out a few words or even a few lines. This is particularly common when scribes are copying lists where each entry has the same beginning.
Memorising these terms isn't particularly important (and there are a few others but they tend to vary in different languages), but understanding scribal errors is taught and studied as an important part of paleography and textual criticism.
As an aside, when I was learning paleography, my teacher used to make us practice sometimes with languages we couldn't read fluently, or at all, so we would transcribe texts in Old Irish or Welsh, or medieval French and German dialects alongside all of the Latin. Transcribing something in a language you can't read is much harder than transcribing something you can understand. I imagine copying something like the VMS, at least at first, is even harder, and more like copying something written in a script system you can't fully read or understand.
A slightly(?) related anecdote: although it's not my major research specialism, I sometimes work with texts written in Old English and Old Norse where the scribes have used runes rather than the Roman alphabet. I can read those languages, but I only work with runes maybe once or twice a year and for the first hour or so when I'm transcribing I'm very slow and I make so many mistakes compared to when I'm working with a text written with the Roman alphabet.