Short form of year

In a table, schedule, graph etc. is it common to write a year like " '07 " for 2007,
or is it better to eliminate " ' " and write just "07"?

For example, which is better, 5/'07 or 5/07?
I would also like to know a shorter way of
"the beginning (middle, end) of (month) or (year)"

Is it common to write as B/May, B/'07, M/May, M/'07, E/May, E/'07, etc.?

Thank you in advance for your help.