I just received an email from someone who's been doing a little research online and found names of a number of (what looks to be) unreleased tracks by Jamiroquai (don't get too excited, it's only track names!).  Have a look at both the BMI (American performing rights organisation) and EMI Music Publishing websites for more information.  Interestingly, most of the tracks I've not heard of only have Jason Kay as the writer.