I can confirm that KLM processed a day of upgrade for me off the GUC waitlist without me doing anything special - by the time I showed up at the transfer desk at T-45 the upgrades had already been processed by KLM staff, even though no upgrade inventory was technically available.

As others have said, the gate staff at KLM have basically no power. For any ticketing or seating related questions, go to the transfer desks - they seem to be staffed with the most capable agents. The lounge agents are hit or miss - they are supposedly empowered to do everything the transfer desk is, but they tell me Not Possible™ much more often. (Not sure if they just get sick of dealing with elites constantly in the lounge, while the transfer desk is more inclined to be helpful because there's a different mix of passengers and they see fewer folks with status there?)