consider this...

The ship is 5 miles long and according to the signs on the walls it has at least 500 floors. Lister ranked 169 of 169 but that may have been for officers and technicians only, it might not have included extra staff who didnt require a ranking.\r \r Also Rimmer has a habit of making all his problems sound worse than they are.

Nitpick is right

In the first scene of the first episode, Todhunter says to Rimmer that 'there are 169 people on this ship, you are but one man, why can't you two get along?', or something to that effect. Also in the same episode when the whole crew is called to the Welcome Back George party, they all fit in to one large room. So, yes, the number of people killed changes.

Maybe...

In Series 8, Red Dwarf has Floor 13 a prison deck. Judging from the size of the place, it is possible that there are 1000 convicts or slightly less plus some special guards, niether of which would be considered part of the official complement of Red Dwarf. So Rimmer was guilty of killing 1167 people, 167 of them were the crew, the rest (convicts) weren't counted as they're not important.

Red Dwarf picked up some personell?

Several weeks went by in between Lister's placement into stasis and the radiation disaster that killed the crew. Maybe they picked up additional personel? It does seem strange that a ship 5 miles long would only have a crew of 169.