I've had a search around and I haven't quite found a definitive answer.
My mother flew with oneWorld back in August (so just about within 3 months)
BA: LHR-(SIN)-SYD
QF: SYD-BRS
CX: BRS-HKG
BA: HKG-LHR
All booked under QF codeshares
I want her to join BAEC so as not to waste those miles, but she she has no clue about the FFP world nor does she want to learn about FFP. She's not got the boarding card for the QF sector, nor does she have an ET reference, PNR or even access to an itinerary (someone booked it all for her)!
I'm not sure what booking class it was in, but I suspect & expect it was Y. (Additionally she got an OP-UP due to overselling in economy which adds to my suspicion)
So I figured I may as well sign her up as a household member. But I noticed the following on BA.com
My child (who is under 18 year old) has recently flown with British Airways but was not yet a member of our Household Account. Can I claim for their flight retrospectively?
Yes, once enrolled in the Household Account you may claim for their flight retrospectively.
ALL new members of a Household Account may claim for BA Miles and/or Tier Points for British Airways flights flown, no more than three months prior to enrolment. No credit will be give for air partner flights flown or non-air partner transactions prior to enrolment.
BA-Your Questions
So am I right in thinking I should retro-claim by post to get her blue membership, then once an account exists, add her as a household member (same address isn't a problem).
Or is there something else I've not thought of?
I'm worried about what happens if I'm wrong and she didn't fly in a Y or B fare and thus loose all miles?
And I can change my account from being a household account back to a non-household account after a year or so as well can't I?