well writing the month is a great idea - heres why..
a few months ago I upgraded my Simply Accounting program for my business.. (each year you pretty much have to buy the program for $280 if you want the payroll updates)

now it turns out I had to upgrade the computer at the same time as it
just ran win98 (this computer was used only for accounting)
after installing everything and printing out a backlog of invoices..
even though my date format on the invoices is month day year - and has been for years.. somehow when it came to printing the operating system switched the dates around to day month year..

of course I didnt notice this until customers called and wondered why the invoices were 6 months in the future.. (some dates were blank
when the format didnt make sense..)
so I had a whole lot of customers to call and reissue new invoices all because the windows xp default date format was different than the accounting programs.. (and instead of notifying you of the discrepancy
the software just goes ahead and tries to print in another format)