This Spirits thing is one of those weird, malleable 'fan' rules that only really exist because it seemed like a large collective of people decided that that
was the rule now, and folks just kinda silently agreed on it. Which is a bit odd, considering that I'm pretty sure there are various Spirits of some of the current fighters that can be found in the overall inventory. But characters like Mario, and K. Rool, and Daisy, they're all still
Fighters, even if they do have Spirits.
Not to mention, this is a video game where the programmers kinda dictate the rules and how the world works. Spirits are supposed to be the ghostly remains of a particular character, and yet, I can get as many Dr. Wily's as I wanted, so even if "one" spirit exists, that doesn't mean there certainly can't be more than one.
It's such a hard, frustratingly difficult thing to debate, considering there's never been an
official declaration, and yet we're all led to believe that it's officially
implied. Which is such a weird thing to say.
I'm going to say for my own personal record that I don't believe that Spirits = Deconfirmation. I feel like Assist Trophies are a much more hard Deconfirm than spirits are, and even
that's not necessarily ironclad considering that characters like Little Mac and Isabelle are now in the lineup.
Each time a new game comes out, more of the supposed rules seem to get thrown out, so for our sake, let's hope the trend continues.