I was doing DL LGA/RSW last year and we were bused from the terminal to a bunch of parked RJs on the field. I was first off the bus but there were several waiting a/c with doors open and the driver never indicated which a/c (although he could have after I left the bus.) To be sure (I was also the first on the a/c) I asked the FA if this a/c was going to RSW. So in situations like this I can see it happening. A normal gate boarding not so much.