I'm new to this so please forgive the newbie question...
I found a boarding pass from a flight in January on Northwest. I was ignorant to the ways of the FF world back then

and didn't have a FF program.
I have emailed NW and it seems I have up to 9 months after a flight to submit my boarding pass.
Here is my question - since I don't fly NW often,
should I / how do I have these miles credited to a different airline? I am doing a Delta/car rental promo and will have 30k miles on Delta before long.
Thanks for any help/advice.