Start and stop times may encompass frames of good data
If two or more afterglows are horizontally, vertically, or diagonally adjacent to one another on a CCD, then the set of afterglows are marked as adjacent to one another, whether they are associated with a common event or not. As a result, the start times of the afterglows in the set are modified to have the same start time, which is the earliest start time of the set of afterglows. Likewise, the stop times are modified to use a common time, which is the latest stop time of the set.
In most cases where afterglows are adjacent to one another, the afterglows are associated with a common event and have similar start and stop times. However, in rare cases, they are not associated with a common event and the start and stop times can encompass many frames of data instead of just a few or a few dozen frames. In these rare circumstances, some good data may be marked as bad in Level=1 event files and excluded from Level=2 event files.