Hierarchical vs. Tags vs. – Common Ground?

After seeing the Johnny.Decimal comment section, I have an example I'd like folks' best solution for. This is a real world example, I deal with this a lot.

I'm a musician, and book bands for a venue. So in a normal day, at my day job hiring bands, my hierarchy looks like this:

poster/$date $bands/poster.img

And when I play somewhere, the hierarchy looks like this:

$band/poster/$date $venue/poster.img

For organizational reasons, it'd sure be nice that when I play my venue, there's one poster, and both hierarchies point to it.

I just don't know of any clean solution to that, where branches touch.