You have to remember that of of the unmatchables, they go through and see if they can double assign before reaching out.
You're conflating two things. 1. Unmatchables are people for whom there are no possible recipients in the entire set of requests. These people will be the same no matter how you run matching and must be contacted to either change their offers or drop out.
2. Double assigning means assigning two authors to the same recipient, which is the flip side of someone being an IPH - they have no writer, so someone else gets two in order to make the numbers even out. Mods don't "try to" do this; they HAVE to in order to send out assignments. AO3 literally won't let them send out assignments until everyone has a recipient.
Re: Matching Game
You're conflating two things.
1. Unmatchables are people for whom there are no possible recipients in the entire set of requests. These people will be the same no matter how you run matching and must be contacted to either change their offers or drop out.
2. Double assigning means assigning two authors to the same recipient, which is the flip side of someone being an IPH - they have no writer, so someone else gets two in order to make the numbers even out. Mods don't "try to" do this; they HAVE to in order to send out assignments. AO3 literally won't let them send out assignments until everyone has a recipient.