Spanish speakers are a huge group and many simply don't know their own language. It's like going to Alabama and expecting to find Shakespeare.
I'll grant you that mutual intelligibility is difficult to define but I'm using it in the sense that my wife is conversational with folks from Portugal and Italy when we travel there. That's a decent standard.
But then I am a poor benighted bastard living in Alabama.
Of course, I lived in Texas until about 8 years ago, when I moved to AL.
Edit: typo
I didn't present numbers because those are hard to prove but I agree with your assessment. Anytime you're over 60% (at least 1-way which is what you were describing, your personal comprehension, not the Italian's), you're in great shape. 60-90% (a low estimate because it's one side) is getting into dialect territory. Simple statements and conversations are not a problem and that's definitely mutual intelligibility. Yes it is a bit of a stretch, but everything in one way or another is a stretch. As a general judgment call I think it stands. My point was, as a native English speaker and conversational speaker of Castellano myself- my English enables me to understand exactly zero other languages. Mutual intelligibility is indeed real in the Latin world. There's little to no mutual intelligibility with English, except maybe to Frisian, I've never heard it in person. But there is definitely mutual intelligibility between the former Roman Empire except France and Romania. I do understand some Italian. Absolutely nothing compared to you or my wife. My wife has the roughly 60-90% comprehension ability you do with Italian.
On the 'mutual' side of mutual intelligibility, from what I've seen educated Portuguese and Italian speakers understand her even better than she understands them. At least, again, an educated speaker who doesn't get confused with their own language first.
Of course there are not. They may not know whatever it is you are talking about, but it's tautologically true that a group of people communicating with a given language know the language they are using to communicate (the language that they would likely refer to as "their own language"). I guess no one will care if you don't want to call that language Spanish (they won't heed your opinion, they just won't care).