How are PDB reference numbers relevant?

See How do I use PDB numbers? in our Invoicing FAQ for an overview of this concept.

Anything on the list of What on-set situations am I required to notify AW HQ about? will likely require a PDB number on the invoice (if it affects what you are charging us for).

Something that only ever happened on one shoot probably requires a PDB number on the invoice (if that thing affects what you are charging us).

PDB numbers are not required for the “standard” things Shoot Producers invoice us for (for example, the fee for making a Solo shoot based on your Level; one model lunch per model per shoot day).