It's 3 months for retro claiming prior to registration, and it is only for BA flights
https://www.britishairways.com/en-gb...and-conditions
14.10. Avios points and Tier Points which are not tracked automatically at the time of travel may be credited later at British Airways' discretion. Members may claim Avios points and Tier Points after completion of their travel either online at ba.com or if required by submitting the retained segment of the boarding pass and passenger receipts provided that the Member was enrolled in the Executive Club at the time of travel and the claim is made, within 6 months of the date of travel or the relevant transaction. A new Member may claim Avios points and Tier Points for eligible British Airways flights taken up to 3 months prior to the commencement of their Membership.