I purchased recently a Nancy Drew Twin Thriller book club edition at eBay - the seller had listed several and included an original letter with one of the books. I snapped that up quickly :) I am in an ongoing quest to amass as much research material as I can about Nancy Drew for my books and writing projects--not to mention my collection!
This letter--if you click on the above image it will enlarge to be able to read it--mentions a few interesting things.
First, I was aware of this book club being advertised in different publications--including some Teen ones. I have an original Young Miss magazine advertising the club in an insert. It was referred to as the "Twin Thriller Book Club" but the letter above calls it the "Parents' Magazine's Nancy Drew Twin-Thriller Book Club" - both the magazine ad and this letter have the same New Jersey address. I suppose it's likely that depending on where it was advertised, it was changed slightly--or it may have been taken over by Parent' Magazine at some point.
Second, the letter refers to them being out of the introductory volumes--which included Old Clock/Hidden Staircase and Bungalow Mystery/Lilac Inn were out of stock so they were substituting Mirror Bay/Double Jinx and Glowing Eye/Forgotten City.
The book I bid on was Mirror Bay/Double Jinx. So I got one of the volumes they were substituting.
I love finding book club memorabilia! If anyone ever has any they're interested in parting with and you happen to come across this blog while searching what you have, please contact me!