My impressions is that during a 40 min exposure, there were 2 N-S tracks. To me that means that over a 40 min period, there may have been 2 satellites with similar N-S ground tracks. They didn't have to occur at the same time (ie formation flying), just pass by during the 40 min period. Also, I question what the estimated brightness is. If the object is moving slow, it seems that it could be dimmer than is being estimated. Checks of satellites going by during the time in question should probably not use brightness as a limiting factor in searching for the possible satellite.