Rumors becoming 'accepted' by industry media
1) The debut rumor that seems to be getting the most hype recently is a dedicated Corvette Debut event, not a debut at a Race or a Show of some kind. Depending upon how you interpret this, the rumor might or might NOT exclude an NCM debut. IF the debut includes some journalist seat times, NCM has a pretty good track that could be used, but not as good as some other tracks with more acclaim like VIR.
2) In a recent post on another Forum an individual claiming to be a supplier for the C8, is saying that GM has notified his business that the C8 production will begin in December 2019. As far as I can tell, no one has been able to confirm or deny the poster's claim to be a supplier, nor, of course, anything about a December date.
Conclusion: Make your own. Flip a coin. Ask your Psychic. Get AOC's opinion (I'm sure she has one). Meanwhile, we wait.