8

They cycle, or at least they used to cycle.

Your experience is uncommon; you should be averaging 3.75 per day instead of 6-7.

I don't know about the averages but I do mine on just one or two toons and ran out also. I started doing my writs in Rawalkia as there are about 10 mudcrabs right near where you turn them in. I just turn them in, spend a few seconds killing a few each day and that solved the issue. Plus there are about eight or nine chests in town that are closely spaced near the crafting stations which picks up an extra 3 to 5k gold or so one each toon.

There are 8 different combinations of request that pair an alchemy potion or poison with 3 ingredients that rotate among each character.

Character 1 will have say Stamina and Mudcrab on day 1 and on day 2 Character 2 will have that quest next and Character 1 will have Magicka and Violet Coprinus.

This being the case and having 15 character you will always have at least 2 characters per day that need Mudcrab and Violet Coprinus and depending on where you are in the cycle 3-4 character every day. The cycle will look like this for 32 days (the X is where a character has one of the 2 quests):



I have been trying to work on an addon that manages crafting writ pre-crafting a little bit better than what is already out there.