I’m not sure if it’s in the audiobook or not, but the very first page of the book that starts out as an interoffice memorandum, she references why she tells this story as a narrative as opposed to the previous dossier.

Also in the same memo she states that she’s adding her conclusions which were requested by Gordon.

Yes, that bit's in the audiobook.

Like I wrote, my opinion may change once I read it, but it seems to me that TP isn't a very reliable Archivist. And the book might have improved (or at least been a bit longer) if every entry included a "just the facts" version, including how Tammy ascertained the information, followed by her commentary, questions and analysis.

I gotta be honest, I don't care much for Frost's writing or narrative voice in general, at least not in the form of a 'novel.' The voice of TP in the Dossier doesn't seem to really match the character as portrayed in season 3.

But no matter, it's the content that I'm more interested in than the style. And there's quite a bit of content in a relatively short book. More than I expected. Even Bad Coop and Jeffries stuff which I need to reread.

I'm still having trouble reconciling the Tammy of the Frost books with the Tammy we saw on-screen. The reticent, off-kilter, unfazed-by-the-paranormal Tammy seems more like yet another eccentric of the type that seem to populate the Twin Peaks universe's version of the FBI. The Tammy of the books seems a little more traditional and skeptical, while more inclined to expand on her thoughts at length. She also addresses Cole as "Chief," something I don't think she ever did on the show. I suppose we can assume that she tends to take a back seat when working directly with Cole and Albert because she knows they're more experienced and probably know things she doesn't, but that she feels a little more free to expound and speculate when using the written word. But it's certainly not the style one would expect based on Season 3 alone.

There are also some chronology quirks in terms of how Secret History fits into the series' timeline which, as far as I can tell, are not resolved in The Final Dossier. If she reviewed the first dossier (from TSHOTP) before the events of Season 3, then how can she not know who Jeffries is in episode 4? And if she reviewed it after Season 3, she's failing to draw connections that should be patently obvious after what she just experienced.

I'm mostly bothered by the disconnect from her character on the show, but I agree that it's not very "professional" sounding at times. But then again, this ain't the regular FBI we're talking about, and Director Cole can be pretty nutty when it comes to it. This is the Blue Rose Task Force after all! It seems more like an independant and mostly clandestine sub-group of the FBI that delves into all the weird, supernatural stuff that no one else would even take seriously.

It's probably why their "offices" in most of S3 were in a hotel, right?
BTW: I really loved that moment when Diane says "Let's rock!" with that weird vortex wind underneath.

I agree, the switch between professional documenting and personal asides kind of throws me.  Probably my main criticism of the book.  If Tammy had been more outspoken in the series then it might fit better, like, I can see Albert writing that way.  But Tammy seems more reserved and straight laced.
I just read through the Dale Cooper "my life my tapes" book and I thought that handled the character tone much better in terms of combining professionalism and playfulness while maintaining character.