So let me get this straight... Super Micro hired a firm, who then asked the manufacturers, "Hey guys can we please have your design files for your PCBs" and then they looked at the parts list and said, "Nope, no dedicated backdoor chips here" ? They didn't really do a thorough examination of the devices in question, but asked the manufacturer for the CAD files?
At some point it is up to Bloomberg to show something. It isn’t possible to show a negative in this case.