The announcement made me wonder whether there are more to be found in MGS's years of photos. Much like how amateur astronomers have delved into the archive of observations from the Solar and Heliospheric Observatory (SOHO) to find comets, maybe some dedicated sleuth will find some craters.
December 7th update: I wrote to one of the team members, Ken Edgett of Malin Space Science Systems, and he notes that there may well be more craters to be found. He said that they only looked at 30% of Mars's surface, concentrating on the dusty regions where the dark splotches would be more pronounced. Scars in other areas may be more harder to spot.