I usually see Xterras with only the center light working if they have lights out. Seen several this way.
How could you figure Nissan was just putting bad bulbs in the right side?
One of mine burned out after 3-1/2 years, but I can't remember which one it was...I have better things to keep track of. I think it was the left one though?
Always a good idea to check them on a regular basis and have a spare or two around.