Originally Posted by
maalloc
I always played it safe and canceled while airport check-in was still open, but I am yet to see any data point that would suggest that AF or KL don't stand by this written rule.
That's why I am asking why you write that they don't stand by it.
You use the phrase "played it safe"; that's also my advice to the OP.
"Before departure" is an imprecise phrase. And what the OP has written seems to indicate they're interested in waiting until beyond 3-4 hours before departure. The OP's interpretation of "before departure" here might end up very differently than what KLM will actually impose; waiting until the absolute last second is always risky, especially when it's not 100% clear when that "last second" actually occurs.
I'm advising against whatever plan the OP is focusing on as it apparently puts them in a position where they won't be able to cancel until so close to departure that it might not actually be feasible to cancel the ticket in time.