I think Lindsey took credit for the "am what I am what I am what I am..." thing in "Family Man" too, but to my ear it sounds way too much like Stevie to be a studio trick. Someone who is extremely knowledgeable about all things Stevie told me it's actually her, and he's usually right. He says it was a Lindsey-led conspiracy to try to erase her from the album, and Warner wasn't having it.
I always thought I could hear Stevie on "Mystified" too, in some parts. It sucks that it's probably not her though.
Mick's book is probably wrong about Stevie's vocals being layered into "Everywhere", I think the ghost-writer did bad research and meant "Little Lies" instead. The background vocals on "Everywhere", like "Mystified", are a shimmering jumble of sounds, you can't specifically hear her. If she's there at all, it's still not the pronounced type of vocal like on "Little Lies" that would warrant a half page in his crappy book.
Stevie's accounts are troubling though. At one point she was blaming her absence from TITN on klonopin, but if she started that drug in 1986 she wouldn't have been on it long enough to cause the type of lethargy and not giving a **** that she was describing. That came later IMO, with BTM and OSOTM.