Topic of the Day:
Disc 2 of "The Hitchhiker's Guide to the Galaxy - Primary Phase," the original radio play. I bought THIS version and it just arrived earlier this week. I have this on vinyl, but none of the rest of the books. Now, I have the complete series! 
Looks like you're the person to ask for clarification on this, DR George.
I never owned any of those originally. Probably never even heard the whole thing. Just a couple of years ago I stumbled upon a copy of The Primary Phase (on the audio cassettes!) which I totally loved hearing after all these years. So what does the complete series consist of? I hate to say it but now I don't even remember how much of the books Primary covered, so I'm taking it out to pop it in for a new listen.
I love these, like I love the original BBC TV version. They captured the spirit of the original work so beautifully in their special way.