If an airport has three parallel runways - a good example being Schiphol (EHAM/AMS) - the parallels are usually labeled "left", "center", and "right", and in case of Schiphol they are 18/36 L/C/R.
However, if there are four or more parallel runways, one or more have to be given a different number. For instance, ORD has five parallel runways heading 93.6-273.6 and their designations are 9/27 L/R and 10/28 L/C/R.
Why couldn't these runways all have the same number and add a second letter - I, M, or O (for Inboard, Midboard, or Outboard) so the number can accurately indicate the runway's heading? Under this system, ORD's 10R/28L could become 9LO/27RO.
Is it because the I and O could easily be mistaken for a 1 and 0?