If I asked someone from 100-200 years ago to imagine a post-scarcity society, I'd expect them to say something like "you can have as much of ___ as you want". Furthermore, I think they'd clearly understand the difference between "have more of it than we get now" and "have as much as we want", whether it's lifespan, food and shelter, or anything else. I don't see why someone from that time period would think a "post-scarcity" society means a society that merely has less scarcity.

"Someone from the past would say our level of something is far beyond what they would have hoped for" doesn't equate to "someone from the past would say that our level of something is post-scarcity". Presuming they speak English and the meaning of the term "post-scarcity" can be explained to them, I don't see why they would confuse the two.