Pat,
Sorry, does not ring any bells with me.. ?
Although anything is possible, but I don't believe that pool popping of gunite pools here in the DFW area happens too often.
If you can dig a 3 or 4 foot post hole in your backyard and it does not fill with water, I suspect you will be just fine.
And... I would not be surprised if no hydro-static valve is even present. I have had two old pools replastered and neither of them had anything but a single main drain pipe.
Thanks,
Jim R.