An Open Letter To Clive Cussler

Dear Mr Cussler,

While I'll admit that I stayed away from your books for many years because I didn't want to be seen reading the same books that my dad reads, I got into them a while ago and enjoy them immensely. There is, however, only one problem.
Recently I read 'Valhalla Rising' in which I was introduced to Dirk's son and Daughter, Dirk Jr and Summer, who were apparently gestating inside their mother (Summer Moran) after Dirk shagged her then left her to die in a subterranean underwater cave-in way back in the events of 'Pacific Vortex!' While she was thought dead it turns out that she survived, was washed to shore and lived to give birth to the two non-identical twins mentioned above.
The problem is, Mr Cussler, that I've just read 'Pacific Vortex!', having tracked it down in my local secondhand book exchange, and Dirk and Summer NEVER SLEEP TOGETHER. Every meeting we see it all in real-time, so there's no point at which they could have nipped out for a quick knee-trembler without mentioning it in the narrative.
Please explain.

Yours,

D C White

P.S. Can we see a return to the use of exclamation marks in the titles? They were cool.