Ann: UK Government lifts moratorium on hydraulic fracturing, page-37

I am not sure about your conjecture but it is possible Cuadrilla does not tell the whole true story. No body know until they frack again.
But my way of thinking as a layman is that if the 2.9 M tremor broke the highly stress fault then all the built up energy and stress force stored in the folded rock over last hundred thousands of years and all the stress energy have been released by the 2.9 tremor therefore the less likely bigger tremors will occur at the same site. Like the energy store in a spring or rubber band analogy.
So if they frack again at PNR maybe less chance of tremors bigger than 2.9M?? But like I said just my common logic not as a geologist. Maybe someone on this forum with more knowledge can fill us in.