That seems weird that if a character buys or makes a vial of poison, tha you can only coat one bolt. Does this mean that a vial of poison has more than one dose? and if so how many doses in a vial.
You make or buy poison by the dose and the core rulebook gives no weight or volume for it, so you can put it in any size vial or flask you want. I might suggest a phial holds up to 5 doses, a vial holds no more than 10 doses or a flask holds about 20 doses.