Your premise of the USPS non-delivery of government checks within a one-week riot being responsible for quelling the riots is ludicrous on its face. Thankfully, such an assertion is not among any of the more respected descriptions of the events. Perhaps you'll point us to some places where such an assertion is made and supported.
HF
The assertion was made here on FR, and we all know what a disreputable place this is. I'll do some digging and find the thread.