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Rich, good question. I use the term "exotic" only in the sense that it is title of the book: "Exotic Amphibians and Reptiles of the United States".
In the Introduction, the authors provide their definitions: "What constitutes an exotic species? Very simply, an exotic species is one whose dispersal is a result of human mediation." And for "native": "A species whose presence is not the result of human mediation".
In the Introduction, the authors provide their definitions of "exotic", "invasive", "native", and "endemic".
Given that definition, the presence of a species in one part of a state could be natural and in another part of the state "exotic". However, the species enumerated are all described on a state wide basis; with some specific locations included.
I did not see clarity of definition if the species had once existed, then absent for X period of time, then "reappeared" via natural or exotic means or new findings. The common snapping turtle would be such an example.
It would be reasonable to consider if fossil evidence constitutes a species to be native even if a current population were human mediated.
My main concern with the book is mostly confined to the discussion for each specie under the heading "Introduction history and geographic range". The pet industry and reptile keepers are not responsible for all the "exotic" introductions. The book does not cast that net over all "exotic" populations; but, certainly the narrative, in my estimation, leans heavily on reptile keepers and the pet industry. Yet the current trend to regulate keeping reptiles seems to have foundation on narratives of "escaped pets" or "storms that demolished the reptile facility".
As noted in the bullfrog discussion, it is likely that much of the "exotic" dispersion of that species came about due to socioeconomic conditions post Great Depression. Although a scam, people were starving and seeking means of support. This notion was ignored in the book's narrative. The use of amphibians in recreational fishing as bait is largely ignored because this activity provides revenue via state license sales. Environmental damage by feral and domestic house cats I suspect far exceeds the damage of pythons in Florida. (I don't endorse either - but house cats are totally ignored by regulators). The vast majority of venomous snake bites occur to non reptile keepers. And so forth.
Finally, the book's authors use several terms under the heading of "human mediated" including "deliberate, accidental" and other terms. In reply, John Zillmer provided an excellent categorization of the terminologies used in the book for how the species were dispersed.
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