Keep Circulating the Tapes: Much of Thirlwell's work may never see the light of day again, due to being out-of-print and not very well distributed in the first place. Illegal downloading and the rare re-release can staunch the losses, but for most of us, we get what we can find.
He's re-released a lot of it, and most of the rest is on compilations, with rumours of another "Sink"-style compilation coming soon.
And as anyone who's looked him up YouTube can attest, this is in full swing for records of his live performances.
No Hit Wonder: Until he was commissioned to provide the music for The Venture Bros., Thirlwell and his work was a rare case of being completely underground to everyone except those who knew about him from other avenues. Didn't stop him from gaining a dedicated trust, however.