Wow, seriously. That is a lot of stones. Do they know what kind of stones? People can have different types and that can give a clue as to their origin. This article goes through the 4 different types of stones. Each one is going to be the result from specific causes. There are calcium stones which happen usually if someone has metabolic issues or renal issues, or on certain medications, OR struvite stones which happen in response to infections OR uric acid stones which happen if someone doesn't drink enough fluids, has gout, eats super high protein diets OR they could have cystine stones which is a genetic disorder where the kidneys excrete too much of an amino acid.
If you know what type of stone, that may help narrow down what your husband can begin working on to help prevent future stones. https://www.mayoclinic.org/diseases-conditions/kidney-stones/symptoms-causes/syc-20355755