Since you haven't given any indication about the specific passenger list I will speculate based on my experience.

Do the entries look like this:
3 - 2
4 - 6
2 - 7

If so, they are a breakdown of country of origin of the passengers on that page. A new set of numbers should appear whenever a new country of origin appears on the manifest. The first number is usually the number of males and the second the number of females for the country next to which the data appears.

To check it out, total the numbers in the first position, it should be the number of males on the page. The second should total the number of females.

You are correct. It has nothing to do with death and was most likely added well after the voyage as a tally of country of immigration.