I got an update notice on my MBA from the Mac App Store to update Sky Safari Pro, which I did. As the documents indicate, the PGC Extension Database and the GAIA Extension Database have been restored. However, I also had purchased the H-R Diagram option, and that did not restore - it still shows as a $1.99 purchase.
I also have Sky Safari 6 Pro installed on my iMac Pro - and got no notice to update. I deleted the app, and then downloaded the app again, and it now also shows the PGC and GAIA extensions as installed. But again, the H-R Diagram option shows as a purchase.
The "Restore Purchases" option doesn't work on either the MBA or the iMac Pro.
My guess is that this is an Apple Mac App Store issue - but I would really like the H-R Diagram.