I have four copies of "Cyclops," each with a different cover. I can say the same about "Sahara," and I've seen many other cover variations for that as well. The German eBay site reveals that all Cussler books have been translated, and many have gone through a series of editions and printings there as well.
To me, this is a matter of interest, but not one of concern. I don't wish to pay more than $.25 - $1 on average for any of these books, and I am most satisfied at the bottom of this range. I am planning to build a guest house and I am considering Clive Cussler novels stacked and packed between the studs for insulation. Well-read copies are abundant enough to get a good R-Value-to-cost ratio (also known as a good R-value-value.) The term "fire hazard" is in common parlance exactly because of designs like this one. I will be sure to remind guests not to fall asleep with lit cigarettes.
I contacted Hyatt of the Cusslermen today for guidance on matters surreal and imagined: