Letter to provide additional documents after test

[Dogdogdog]

I read somebody receive letter to provide additional documents after test.
What are differences between the letter before the test and after the test?

 

[Katayoon]

I read somebody receive letter to provide additional documents after test.
What are differences between the letter before the test and after the test?

The first is usual and the second is less common.

Everybody gets letter before test - it lists documents to bring (usually the originals of the same docs you copied with your application).
Not everybody gets letter after test (most people don't) - they send it when they have doubts and need additional proof, e.g. they may ask translation of passport stamps to confirm you met residency requirement (if you have stamps in arabic, farsi etc.with different numeric symbols for dates).