Originally Posted by
mechu
Under 3.3 of Finnair Rules, it says "Finnair Plus points can be collected only after membership begins". I am assuming it will be alright if I sign up as an AY member the day before my flight?
Yes. However, there's no reason not to sign up today.
Originally Posted by
mechu
See that aa.com allows me to add my AY membership number under passenger info. Do I still need to give the agent my AY number again when I check in for my flight?
You can offer to give it at the desk, and the agent will let you know if it's in the system already. If you OLCI, you will see the number on your BP, and in that case there's no reason to reenter the number at the desk.
However, if you have another number in the booking already, then sometimes it seems to take two steps to change the number. First you remove the first one and save changes. Then you enter the new one. Otherwise, it may not stick.
The BP is key here, so check that you don't end up with a BP that shows the wrong FF#.