Daa daa! My final conclusion!
After months of searching, I found the answer.
Luckily there is a blue dial buyer in Canada facing the same issue like me. And he checked his blue dial 6694 with Canada RSC.
Good news is the blue dial 6694 is real and it just discontinued from 80's onwards and there is no blue part available from Rolex nowadays.
Attached herewith the link and write-up printscreen.
https://www.rolexforums.com/showthread.php?t=208710&page=2The takeaway from this case:
1. The winking smile salesman is telling the truth. Don't just people by their looks.
2. The professional watchsmith could be wrong due to he is not getting the full set Rolex reference record books. The judging on 6694 authenticity by using the latest 80's is certainly insufficient and misleading.
The result: I am a happy man. Although my blue dial 6694 is not yet registered with RCS and not sure it is using Frankenstein original blue dial or not.
But what really matter now is Navy Blue Dial 6694 does exist and I am happy about it!