Unfortunately this isn't an exact science. Alan_A2 has spent a lot of hours researching A2 production numbers that has confirmed that for the UK at least - specific data for tone of colours is not available. It's to do with the quality of the information supplied to DVLA.
Rejoice in the fact that cobalt is not common. ( subjective statement). Just how rare it is you may never know. You may be able to find out from Audi how many of your paint code rolled off the factory floor.
But hopefully take solace that in 8 years of A2 fancying - your car is the second cobalt one I have seen.
Slight swerve again on this post as I guess it should go in the 'What colour would you choose' thread, but anyway just thought I'd take this screenshot of Autotrader search page for A2's, Blue is definitely still out there with Silver a close second, no Yellow 'Mike' A2 Sumo' you'll be pleased to see, appreciate this is only one port of sale but be interesting to see how it looks in another 12 months, and I also appreciate there are a few different Blues!
Cheers jeff