Years ago the present 03/21 at YPPH was known as 02/20. The name was changed, in the mid 1980s I think, to try and avoid the confusion of having too many to's/2's/02's/20's and the resultant cockups due to misunderstanding or mishearing ATC instructions. This despite the fact that there are many other R/W 02/20 combinations elsewhere that seem to function well.
Cheers,
BH.