Glad to see your 1972 stamp guide found a home! I had one of those back in the day, too.
In fact, to fast forward to 2011, I went to my local post office trying to get the latest edition of "The Postal Service Guide to US Stamps", and when I asked about it, two postal clerks looked at each other like I was from another planet ... they never even heard of it!
By the way, you should NEVER even think about throwing out a FIRST EDITION of anything! Although this may not be worth much monetarily, it's currently going on eBay
for as much as $15, which is well above the initial purchase price, if I recall correctly.