Iirc, for those interested, it’s actually a mistranslation of the original Hebrew term.
The original term is tzelas, which is a bit ambiguous.
It could be rib, but no real way of knowing.

https://www.reddit.com/r/AskHistorians/comments/1321fhe/comment/ji30zz0/

I’d argue that durability isn’t the same as AC.

Also, I feel like a plate could withstand a knife stab.

The trick is to get friends to play games with.