Answer?
Assuming you know all switches start in the off position: Turn the left switch on and leave it for a while. Then switch it off and turn the middle switch on. Go upstairs.
If the light is on, the middle switch controls it.
If the light is off, feel the bulb. If it is warm, then the left switch controls it. Otherwise, the right switch controls it.
It's funny you have to specify the year, now that LED bulbs are becoming the norm! (and CFLs before them)