Is "all together" a valid alternative to "altogether" in US English? [closed]

I'm British. I am editing a document, and I was going to correct a use of "all together" where the author clearly meant "altogether" (as in "entirely"). But then I realised this might just be a British distinction... is it? Do Americans accept "all together" as a valid alternative to "altogether", i.e. "entirely"? (The document is for an international audience.)

All together: in a group (a phrase of ALL) "all together, class" Altogether: an adverb meaning completely, totally, wholly, etc. "I am flustered altogether"

Personally, I think the distinction is pretty straightforward whether British, American, Australian ...