It would presumably be able to detect a massive increase, yes, if by "massive" you mean something like a 10x increase in rate. One could do a power calculation

It would presumably be able to detect a massive increase, yes, if by "massive" you mean something like a 10x increase in rate. One could do a power calculation to determine its ability to detect different sizes of effect. Normally you'd do that when planning a study to determine the sample you need, but here they took every available patient in the medical records database they had access to, so they didn't really have a choice of sample size.