Criteria for Statistics Column 

Hi there,
I am very confused with several things in statistics column. I couldn't find any specific criteria for this section. Let me clear one by one easing to answer

1. Month/Year of statistics
Which month the stats should start?? In metro airports like BLR, MAA, HYD and CCU, it is mentioned from April 2010 - March 2011. But in DEL and BOM, month is not mentioned.
When to update these stats?? Monthly or Yearly?? In above mentioned airports, it is still until March 2011. Lets say if it is monthly, how to do after one financial year?? In first month, April only and in next month, April - May??
May be this is silly question, but just to clarify. What phrase we should use for Month/Year. I found several methods. They are April 2011, Apr 2011, April '11, Apr ' 11. Which is better to maintain a standard format for all airports in India??