In the original Techron studies, as well as engine testing in labs, there were trials performed on Chevron employee cars. A couple of really old cars ended up with mechanical problems due to dislodging of crud in the fuel tank.
Your cars are not that old, but it's still possible that it has worked and dislodged something.
Having read the original technical paper on Techron several times, overdosing does not have any real benefit. It is best to let the Techron work gently, and the recommended dosing is based on their scientific findings.
Now that paper was first written a long time ago. Engine design has changed, engines are different, fuel is different and even the formulation is different.
I can say though that it works. I have been using Gumout All In One over the last couple of months and everytime I used it, there was an improvement. I am currently on my third treatment on a car that was neglected and will stop using it when I stop feeling an improvement.
My logic is that if the recommended usage is every 3000 miles (and this is borne out by the science), then if you've gone tens of thousands of miles without top tier and / or doing short trips, then it's going to take more than one treatment to fully clean.
