> The letter I, for example, would be referred to with the phrase I per se, I, which means in Latin "I by itself (is the word) I." When the 27th quasi-letter & was referred to it was called & per se, and, meaning "& by itself (is the word) and." That read as "and per se and."

This explanation is mixed up and confusing. It isn't "I per se, I" that is somehow "by itself I", it is merely "per se I". The reason you get another "and" in front was because it was at the end of the alphabet song: "[and] [per se &]".

https://en.m.wiktionary.org/wiki/ampersand

> Thus the end of the recitation would be: “X, Y, Z and per se and”. This last phrase eventually became ampersand, and the term was in common English usage by around 1837.