Originally Posted by Mwenenzi

Sounds like "not want to be bothered". Have they signed up? Avios?
Have never read of date flight booked vs date of flight vs date joining ffp being an issue with any ffp.
Generally you can retro claim after a flight
But different ffps have various rules about claiming for flights before sign up. Some allow to claim for flights taken xx days prior to sign up. Others do not allow that.

With BA can claim for flight taken 3 months before sign up---> https://www.flyertalk.com/forum/brit...irst-time.html
EI avios may be different.