Resurrection

From my observations, Resurrection works a little differently on Nalan compared to anywhere else I have visited, in that it is not always as successful as one might like.
The key difference between this world and others is that ressurective spells here are not always successful - more specifically the chance of the success is directly related to the worlds proximity to the Darkening; the closer you are to it, the less likely the spell will be to take effect.
During the month of The Darkening no ressurective spells can be used. Or more accurately, they will have absolutely no effect. The further away one gets from the darkening, the more likely a resurrection is to succeed - for instance on the day 6 months from the darkening, the furthest point from it (the day is referred to as The Apex by the locals, and is something of a national celebration), all people who die on this day can be successfully resurrected, with no chance of failure.
Knowing how likely it is to be able to bring someone back is not an exact science, yet it appears to also have something to do with how long someone has been dead for, with spells such as Revivify always being much more successful than more long term spells such as Raise Dead.

Localization

There are rumours that if a body is bought before The Skirling the resurrection can be a success regardless of when the corpse died, however I have been able to find no hard evidence of this.