I was certain a couple of PDFs have been updated at point releases.
Impossible; the integer (X.0) is incremented when the main book is updated, not the other way around. Here's how it works:
A book is published; it is designated Version 1.0.
Errata is found and compiled. If only minor issues are discovered, there might not be any compilations. If big bugs are found, "between-printings" errata compilations will be issued as 1.1, 1.2, etc.
The book comes up for reprinting. At that time, the current errata compilation (if any) and any outstanding issues the devs are aware of are folded into an updated document; the printing and a compiled errata document are designated Version 2.0.
Any further issues are collected as errata compilations 2.1, 2.2, etc.