Why did so many claim to be the last to leave the library?

I'm currently rereading parts of the 11k and one thing I've noticed is how many of the library survivors claim to have either been the last to leave or one of the last to leave the library. Is there a particular reason for this?

I assume they might have thought that due to all the confusion, smoke, fire alarms etc.  I have found that the witness reports vary from person to person. Some things they saw or heard are different from other library witness accounts. But remember these kids were all in various sections of the library. So depending on where they were hiding, they may or may not have seen the others exit.

When exposed to trauma, your brain tends to block out "unnecessary" details. Many of the injured claimed to be the last to be shot for this same reason. Once you've been shot, your brain blocks things out so that it's able to focus soley on the most pressing matter, the fact that you've been shot. So someone being shot across the room from you wouldn't register as clearly as it would if you hadn't been shot.

I'm assuming that, similarly, when you're in shock in the middle of a traumatic situation, your brain would automatically filter out people and objects that it considered non-threatening (in this case, it would block out anything that wasn't a person holding a gun, so that you could more clearly recognize a person with a gun if they come into your line of vision). So that would make all the other people in the room "unnecessary" details and you may not even realize they're there. So you could leave a room full of people and literally believe that it's empty.

I'm not a phycologist or anything, that's just my guess.