Tag wrangler here. I'm not going to log out to double check but I'm pretty sure this is something I've been doing since before I became a wrangler.
1. Go here http://archiveofourown.org/tags/search
2. Type in what should be the name of your fandom or the name of the character(s) if you think the fandom name will end up being changed to something else.
3. If there have been fics posted to AO3 using that fandom/character(s)/relationship(s) or freeform, they will show up. The (#) at the end tells you how many works use that tag.
4. Depending on which of your fandoms do or don't have fics in conjunction with which of your characters do or don't have fics, this is how you can shake and narrow down your unwrangled fandoms.
Re: *shakes collection*
1. Go here http://archiveofourown.org/tags/search
2. Type in what should be the name of your fandom or the name of the character(s) if you think the fandom name will end up being changed to something else.
3. If there have been fics posted to AO3 using that fandom/character(s)/relationship(s) or freeform, they will show up. The (#) at the end tells you how many works use that tag.
4. Depending on which of your fandoms do or don't have fics in conjunction with which of your characters do or don't have fics, this is how you can shake and narrow down your unwrangled fandoms.