A jumper is a bad example, because it’s not just made up of sleeves.

A bra is a much better example. But I was never making an argument that all things made up of two parts are referred to as a pair, just my thoughts on the rationale behind cases where we do.

I’d say it’s less of a grammar rule and more about how things made up of two similar parts can be conceptualised

They’re made up of two similar parts which form a pair, unlike a jumper

Cuneiform is wild. I did a semester of Akkadian on my year abroad and it was very cool, but even people who have spent their whole adult lives studying it still can’t read it easily because of how convoluted it is. We had to learn to read something like 60 ‘basic’ symbols for the exam (although we still got a cheat sheet in the exam), which were just consonant-vowel symbols, but there are so many symbols with so many readings to learn, you would have to dedicate your entire life to it.