So the book I've been reading turns out it's a spin off series.

I got to 50% in and the h/h decides to visit a couple from a previous book. So I stopped but then read a few more pages that was gave several spoilers then as I'm trying to get past this part a huge spoiler comes up and I close the book before I could read it.
Now before I started this book I checked the author's site, several places and not once anywhere did it mentioned this was connected to another series.
Why do authors do this? A note, a disclaimer something to alert me but nothing.
So now I'm on book one which is 6 books behind the one I was reading. A little frustrating to say the least.
Sent from my XT1528