Staff at Geneva thoroughly confused
 

I was booked on KLM 1924 out of GVA at 720 as part of GVA-AMS-LHR-DTW. Boarding was to take place at 650. At around 710, we receive and announcement of a delay and 725 an announcement that the flight was cancelled and to return to the ticket counter for rebooking.

I get in the elite line, as I'm flying business class and simultaneously start messages to the twitter KLM team to try to get rebooked through them. KLM twitter tells me the flight is on schedule. This is at 733, well after our 720 scheduled departure time.

The woman working the elite counter says they're only handling rebooking for elite members and to go to the priority line at the baggage check ticket counter. We're then told to go to the baggage claim to pick up our luggage. Then told that the flight might not be cancelled and to wait. Another passenger sees my ticket and another man's ticket and says we should be in the shorter elite line, which the staff at the baggage check counter agrees.

I switch lines again and we're told after about 5 minutes flight is cancelled.

I end up getting rebooked on GVA-CDG-DTW, and only delayed 30 minutes.

While waiting in the lounge I meet another passenger who had a 90 min later flight to AMS that he missed and had to get rebooked. Because when he arrived to check his bag, the staff was just saying cancelled flight to Amsterdam. And he, along with at least 1 other passenger thought it was their flight.

By the way the crew on the Delta flight is A+. I'm glad to be on it, but I would have appreciated better communication from the staff at GVA.
/end rant

And another thing. After I was rebooked, at 805, I go down to the luggage claim to get my bag for rechecking it. There's maybe 30 passengers down there and the luggage had not arrived yet. It would finally arrive around 830.

The aircraft that would do KL1924 as the first flight GVA-AMS on the 14th came in the evening of the 13th as KL1937, aircraft number PH BGG. That aircraft apparently left only the 15th under an unusal flight number. Can only guess, but maybe an ill crew member or technical issues. GVA is an outstation with contracted staff which may have added to communication problems if the flight would go or not etc. The people running the twitter account probably did not know about the problems leading to cancellation so close or even after your departure time - as your story indicates apparently there was hope they still could fly well after original departure time. Good to see that the damage in the end was only 30 min delay.
https://www.flightradar24.com/data/aircraft/ph-bgg