Sorry no it wasn't Carls guide, I believe it was the small book guide that came out the same time as the base game...
I have read what you wrote in other guides on the internet, but it's not accurate. I can attest to that personally. Before I found Carl and Pam's, I've tried this method many, many times, and it fails as much as it succeeds. Since finding this guide, I have never failed to have a child of a specific gender when I followed the procedure laid out here. Not once.
The popularity of this inaccuracy is likely due to the writers of the first internet guide engaging in a bit of "copy-pasta" in an effort to be the first to get the information up (possibly even from the book you mentioned). Thus, the inaccurate information gets propagated as the copy-pasta gets copy-pasta'd on other guide, and on and on, ad nauseum. It wouldn't be the first time that incorrect information has gone viral like this. And it probably won't be the last, either.
We have a thing about accuracy on Carl and Pam's...almost to the point to where it borders on an obsessive/compulsive disorder. We do not post anything in the guide unless it has been thoroughly tested and checked. More often than not, our members report typos and notify us of poor wordings in the corrections forum more than they do inaccuracies. This is not to even mention that you'd be hard pressed to find someone with more nooboo experience than Pam. She's the Dr. Spock of the Sims world.
Since this thread has been resurrected, I wonder if this works for horses...