Initial death reports are always WRONG. You need at least 24 hours to get an accurate list of who was in the area, who was accounted for (alive and dead), and who was missing.
Then you check for double entries in both categories.
Remember, a lot of kids dove into the river to escape the shooting. Some were killed on the shore or in shallow waters. Those who might have escaped to deeper waters would not have turned up immediately because they might have swam to the mainland or had been picked up by a boat.
When they got to land, then they would report to some authority to say that they were alive. Also, they would tell the police who they saw killed, wounded, or who might have been killed (i.e. sank beneath the waters and did not surface - but could have without being seen. Thus a double entry situation).
Be glad that he figure was revised down, not up. So many innocent people killed by a nut. Every life saved is a blessing.