Matrix,
I can confirm that you are correct, for the 50 hour IR course you just need to have the CPL and MEP skills test passed, you do not need to have the ratings/licenses issued. On test day you will just need to present the skills test pass certificates (forget the correct name but it is the white A5 sheet that the examiner gives you at the end of a test) that shows you have passed CPL and MEP.
Also some schools would allow you to do the MEP skills test on the 170 assessment flight at the end of the IR course. Therefore you didn't necessarily need to have the MEP rating passed prior to commencing IR training.