&? Can we use this rather English short for "and" in Latin? Roman people didn't know it. Hm...
Moreover, it doesn't fit here... if it is to be "et" in Latin...
The sign appears in the text itself (many times), which is from the 15th century, meaning that at this relatively late stage of the Latin language it actually exists in that language. Or maybe the author borrowed it from Spanish, which is his nationality.