I just recently had Avios from a flight I cancelled back in December suddenly credit this past week. Telephone agent said that there would be no problem, even though it was within 24-hours as I had a weather delay, and had declared a 'Trip in vain'. She did a 'reschedule' so that the flight continued to show up as a booking. A few months later I got an email that my claim had been denied.
Then, suddenly I got credit. I'm happy about that. Though it did take quite long.