I think most carriers encourage people to reapply after a certain period (6 months typically). We all know how different the industry is now, but back in 98-99 I had a couple of friends go for their 3rd interviews at United. IIRC one got hired after that interview.
Around the same time I sat on the interview board at a smaller regional. We hired a guy who was there for his second interview. He had a good attitude and decent expereince. I think his first time around he was just a bit green (I wasnt interviewing then).
Just becasue you arent sucessful in an interview doesnt mean a carrier wont hire you. Unless you were a complete bonehead in some way it may just be a case of 10 interviewees for 6 positions. Not all employers use the pool system, some just interview when they need to hire.
Either way it cant hurt. If you get called for a second interview they obviously saw something in you the first time around.
Good Luck!