filled the form out the form on Saturday Jan 4 about the delayed flight/missed connection in the US back in October (flight arriving to LHR from Charlotte was late), received an offer of 600Eur Sunday even though they never specified the cause for the delay ("In accordance with international regulations, we are offering you a check").
I think that the airline knows its liability and maybe it is even better to wait a bit filing the claim so that the the delay is properly recorded in their system.