I learned this the hard way.
I've had iDine for years but only got a UA Visa card in 2007. When I got it I signed up under my word address and First Initial Middle Initial Last Name to qualify for a big bonus. I then went and entered the card under my original iDine account where I'm an Elite. Sadly, I forgot I had the other account and when I used the UA Visa card last year, I only earned 3 miles per dollar instead of 5