I probably missed this in the AP, but are Wati citizens that currently die buried in the Necropolis or only those that died during/before the plague?
As far as I understood it it's new dead as well as old.
As I understand, people up and down the river who can't afford a burial send their dead to Wati where they can find a cheap tomb in the Dead City. There are also specific sites set aside for particular groups and guilds. But noble families around the city might prefer to have private plots of land outside the Necropolis where they bury their ancestors, rather than use a makeshift tomb made out of an old shop or something. The Pharasmins do a yearly procession, but they keep doing interments year-round. The undead overrunning Wati in Empty Graves have to come from more than just mummia traffickers. In my game, the fact that the Pharasmins haven't been able to keep interring people in the necropolis because they're too busy overseeing the Lottery is a major point of contention in the Grand Mausoleum. So when the Ka Pulse hits, all those private mausoleums start disgorging their contents.