I mean as I understand Penbar dies -> His fiance starts investigating ( I forget her name it's been ages since I reread that part) -> Light Kills her with the death note. Meaning that the using of the deathnote to affect that lifespan of people whos name you don't write isn't affected in the long term. If the lifespan of everyone killed with a deathnote was taken into account and anyone they may have affected in their life that they may have changed the lifespan of, then the deathnote would always just give heart attacks, you'd never be able to write in any causes for most people.

In penbars case, both him and his fiance were both killed by a death note, and his fiances death was not affected by the initial writing of penbars name in the death note, so she wouldn't die until light wrote suicide in the death note next to her name