Its a very fine line…and sometimes very registrar dependant.
A Controlled copy is always at the correct/latest revision level. When a change is made, it is retreived and replaced.
An Uncontrolled copy is a bit harder to get you hands around, and is where the variation comes in. Other than it is not replaced when a new rev is issued…it could mean anything.
What you need to do is define each for your purpose, and control accordingly.
Personally, I wouldn’t use an uncontrolled copy for process/acceptance of product unless there is a mechanisim to verify it is at the latest revision.