RE: Why July 15?
IMHO, I'm not sure BBD decision makers feel the heat about the workers deadline of July 15. They need the signed contract first from the customers for the Cseries. No contracts, no CSeries for now.
From what I understand, one key customer is China airliner, who meets for an approval on July 14, from the Government. it doesn't mean they will get it right away on the July 14. You know bureaucrats.
The workers want the Cseries in Montréal, it's not few days, if the NR is done at the UK airshow, that will make them change there minds about the labor contract. The only thing that matters to them, is to keep there jobs.
It would be great to have the GO on the Cseries on the 15, but I'm not sure that it will be THE date. But that's only my the two cents estimate.
Take care!