That's my blog you're quoting and in no way does it support the assertion that it's "been coming since June 2008".
iRacing always announce the cars well in advance of launch and the Corvette is no different. From the link, iRacing explained they had access to some new data which they wanted to incorporate into the car which would presumably make it more accurate.
If you don't like iRacing fair enough but don't make things up eh?