[Think free or die]

"Maybe 3 + 3 = 5 now equals five? "

I don't imagine the bodies were in very good shape after so many years - just bones, which were scattered further during the process of getting the cars out of the lake. Once they got a closer look, the investigators probably realized they had 6 sets of remains rather than 5 and the story was revised.

[AppyPappy]

Maybe one was still alive