As an update, hopefully it will help others.

After going back and forth with KLM on twitter, and them insisting there was no space on KL1443, and that I cannot be booked on it. I literally went through the online "change my flight" process, and sent them screen shots of every stage, including selecting an EC seat and hte payment page. Then my booking was magically changed.

Honestly it was ridiculous, clearly they did not want to move me to this flight, I have no idea why, but the insistence, and strange verbiage, makes me wonder if there is far more at play than availability.