I remember once somebody telling me that the difference between souls (SOB) and persons (POB) was that the former included any 'souls' ie living and dead! and the latter only the living.
the reason being that there was a crash of a mil transport carrying 10 POB, and when the rescue crews went into evacuate those onboard there were 3 crew and 7 coffins
.
I believe that this is the reason there is now a distinction between the terms.