I installed Birthday block in moodle 1.9.5 and setup the dateformat for EUR. I posted the birthday date for some different users to test it.

user1 - 19.07.2001
user2 - 20.07.2005
user3 - 19.07.1999
user4 - 20.07.1994

As you can see the date format correspond to EUR.

I also setup block_birthday_days = 0 to show birthdays of the day.

1st Test:
On july, 19 I tested the block and I found something very strange: Only user1 was listed in the birthday block. As you can see above user3 should be listed too, because they share the same day and month but different year.

2nd Test:
I change the block_birthday_days = 1
Then (on july, 19) the birthday block listed two users: user1 and user2. This is right as they are in the interval of one day. But user3 and user4 were not listed as they were expected because they were born in identical day and month but in different year.

The birthday block worked as expected for EUR dateformat only if the year is 2000 or later.

3rd Test:
I change the dateformat to ISO and changed the birthdays of the four users (user1,..user4) to the new format: YYYY-MM-DD.

Right..!!The birthday block worked as expected.

I didn't test USA format.