Yes, you can add your Aer Lingus AerClub (Avios) number to an existing booking, but the process depends on whether the flight has already taken place. If you have an upcoming flight and forgot to include your frequent flyer info, you can log in to the "Manage Trip" section on the Aer Lingus website or app and enter your details to ensure the points credit automatically after you fly. If you have already completed your journey, you can claim "Missing Avios" up to six months after the flight date. To do this, you must wait at least seven days after travel and then submit a claim through the AerClub portal with your flight number, date, and ticket number. It is important to note that you can only earn Avios for the person flying; you cannot claim points for someone else's ticket even if you paid for it. If you booked through a partner airline like British Airways, the process is similar but may require using their respective portal. Keeping your boarding pass until the points appear in your account is the best way to ensure you have the necessary documentation for a successful retroactive claim.