I see a lot of people refer to those as prototypes, but from my understanding, those are around 80-95% complete.
Aren't those more of just betas, or just unreleased versions? demos? (then again I see them referred to as demos and prototypes in the same sentence most times)
What are those actually called? I'm not sure prototype is the right word...?

I don't have time to look it up right now, but I always figured they came from either the Nintendo Power Station + flashcart or from the BSX Satellaview download service.

They aren't from the satelleview download service, those carts are different. Also, the satelleview came out in 1996 or so, whereas those carts are from 1994. I'm not sure what the Nintendo power station is unfortunately, I'll have to take a look at that.
edit: I'm unaware of it by name at least
 

Do you mean the taikenban (trial version) sample ROM cartridges?

Yeah, those are what I mean  

I'd think those would be categorized in a similar group as stuff like demo discs based on pre-final versions of games, or maybe like NFR carts containing pre-final content instead of as actual "prototype" cartridges.

If they were effectively the same as demos then why are they so expensive? Just the aspect of them being demos for an snes?

Because they're rare versions of popular games that people like, and they're cool.

that makes sense. Thanks  

Some prerelease versions, like the Chrono Trigger "demo" cartridge, contain content that got deleted before the final release.  https://tcrf.net/Proto:Chrono_Trigger_(SNES)

That's fair  
Thanks.