So I added 2 new properties to the devices, release year and pixel density. No real motive here other than adding more data. Right, I forgot to add it to the xml schema definition... good catch. I will get the definitions in there shortly.
As for release year vs release month vs release second... release year just makes sense and it's useable. Remember, defaults are bad and can be dangerous, so I would caution against tagging devices as being released in January as a default.
