HI Dave,
Unfortunately as Derek said, the PDF versions of the GP Documentation hasn't been updated since 2013... Instead Microsoft decided that it was more efficient for the updates to put online in the "Docs" site were all other Microsoft user guides & setup guides are residing, just to make it simplier to maintain.
Sadly, this online documentation doesn't print too well out in PDF format, as I tried once and it generated a 1000+ page PDF file which would just contain everything, and pretty badly formatted.
Gone are the days with the nice PDF user guides, which I agree were probably keeping one resource full-time busy to maintain it and do all the corrections/updates.
The PDF files were nice when a customer was asking for training about a specific module in GP, so you could just send it to them.. on the other side the online documentation allows for more agile updates and flexibility... Guess we all need to adjust to the new reality.