Well, this is interesting. When I bought UFO & Outer Space #23 a little while back, I also purchased UFO Encounters. There appears to be a certain degree of confusion about this title, and no solid information on the GCD, so I figure I should post about my observations.
First, the GCD lists two different "books" in this series, with this as the second. I am almost 100% certain this is inaccurate. This book appears to have been published in 1978, and I would wager it is the UFO Encounters mentioned as being listed in a March 1978 issue of The Comics Reader. For one thing, it is cheaper than the other "issue" - $1.00 vs. $1.95. Yes, it has a higher "number" than the other book, but I don't think this Golden Press code is indicative of which book came out in what order. I mean, UFO Mysteries is promoted on the back cover of my book as the "Volume II" of UFO Encounters and yet it has a code number that PRECEDES Volume I.
Without having it in front of me, I can only assume that the other UFO Encounters is either a second printing of the first edition or a repackaging of the earlier book with UFO Mysteries. In any event, these are books from the Golden Press side of Western Publishing that reprint material from UFO Flying Saucers from the Gold Key side. Given the timing, you can only imagine how they arrived at the title.
I'm curious if this was marketed as a kid's book or if it was more of a general interest SF title. I mean, sure, it's comics from Golden Press, but it's not really obviously a "kiddie" book. I almost think this MUST be a children's title given the era, but would love to know more about how it came about. It's very intriguing in that it's an ancestor to the "trade paperback" that is so ubiquitous in comics today. It even presents the reprints in sequential order!
About those reprints - as I alluded to earlier, they are all from the UFO Flying Saucers run. More specifically, they are from #1-#3 in their entirety, with the first two stories from #4 thrown in at the end. Why? Well, the contents page gives the explanation - it includes the contents of both this book AND UFO Mysteries. That volume seems to finish off #4 and go through #7 of the comic book series. Of course, I wasn't able to score a copy, so I cannot confirm this.
The reprinting is kinda fascinating, in that you have to figure Golden Press had access to the best available materials possible. And yet, comparing them to the original comics (I own a copy of UFO Flying Saucers #3), the collection comes up short. That may be due to the cheapening of comics printing in the intervening years, but who knows for sure. The indicia has been eliminated, replaced with amusing alarmist blurbs. And there is a whole lot of redundancy, as when the Tunguska event of 1908 gets covered twice within 12 pages or when we see multiple versions of Ezekiel. It's probably amazing it didn't happen more, to be honest.
The stories start out as straight dramatizations of UFO reports, but then in subsequent issues begin to slide even further into hysterics. They are all kinds of entertaining as a result. I may discuss a few in the future, but suffice to say, this book is worth some cash if you spot it.