Create a sanbox of 20 users where the tests can be run prior to being committed to the real test.

Pretty sure no other SaaS performance testing tool has this either. The problem is that you would either have to run a very long verification with a single VU consuming data, or a shorter verification with many VU's consuming data. Either of these cases would be creating cost for SmartBear. It would be easier/less expensive if a process merely validated certain things about the data (such as no illegal characters...etc.). Unfortunately, the kind of data errors you are describing, could only be checked by actually having a VU use the data in server requests.