Nearly every shale well from the biggest dogs in history through...

Nearly every shale well from the biggest dogs in history through to the best producers ever have 'traces of gas during initial flowback'. A really good well would give them a flow rate straight away, but during the clean-up process (not flowback) the idea is to literally prepare the well for the next fracture stage, which is what they are doing now, so it's usually just a very short flow to cleanup and depressurise so that wireline can easily set the plug. Actual flowback results in the first week or so will tell the story. Then if it has a sustained flow rate, the sustained production test over a multi week or even month period will dictate the size of the prize i.e. reservoir size.