Not my territory (I'm Suffolk, UK) but big black cat sightings follow a pattern I find really interesting wherever they pop up. Third sighting in a month in the same area is significant - that's not coincidence or misidentification, something is establishing a range there.
Over here we get the Beast of Bungay type reports fairly regularly and the one thing witnesses always agree on is the size. People know the difference between a large domestic cat and something that comes up to your knee at the shoulder.
What direction are the sightings coming from, like is it following any kind of natural corridor - river valley, tree line, that sort of thing? I always wonder whether these animals are moving along specific routes. Would be worth plotting on a map if you've got the locations. Someone local keeping a proper record would be dead useful for spotting a pattern over time.