The Detective Book Club, as far as I can see, was never a reprint
series (unlike Black's Readers Service or Classics Club). The three
books that appeared in each month's volume (if they were monthly; I
don't even know) were always "current" mysteries, recently published.
None of them that I have bears an actual publication date, just the
copyrights for the individual novels.
Yes, the limited edition could have been done at any time, but the
existence of ordinary members' copies makes me believe they were
issued close together. I can't imagine them doing an ordinary member
edition in (say) 1970, and then a limited edition in (say) 1985. And
what possessed them to reprint these three novels at that time? And
while I'm asking rhetorical questions, how limited were the Zane Grey
"limited" editions? (Were they numbered? I can't locate one on
Bookfinder to check...)
But yes, it's all supposition, since--unlike the Zane Grey page--there
seems to be no site or documentation on the Detective Book Club.
One of the great living treasures of the bookcollecting world is Steve
Trussel and, no, he doesn't quite fill the gap you note. However, he does
have a page on 2- and 3-in-one Detective Book Club editions of Maigret,
which seems to bear out your observation:
As far as I could see, all the Walter Black Maigret was published fairly
shortly after it originally appeared in English translation.
I found one or two listings online as well, such as this one -
- which seems to be "current", but you
could probably get a better idea by chcking through the ABE listings to see
whether there are any exceptions listed there.