well I don't know, I once failed an interpreting school's very simple interview
in my A-language ( I do not wish to name the school here on the forum but it was a very easy school to get in!) because of a weak A-language ( I was not even aware that my A was weak until after the exam), the following year I passed the same school, but failed my C-language. they had not told me the first time around that my C-language was weak too, so I did not even know.
Then I took another school's entrance exam a year later and failed all parts in the oral exam (I passed the written part, surprisingly, with all languages, ABC) , but I didn't know whether it was A/B/C-language related my failure, but I strongly suspect that it is related to mostly the A-language, and a bit the C as well.
I am now in the country of my A-, read papers all the time, watch and listen to news all the time, etc, but I still make mistakes that another native speaker who has not spent that many years abroad would never make.....(so I was told)
small mistakes that can only be detected in a complex conversation about a certain topic, not just "hi, how are you"...
and once a EU interpreter spoke of a so-called "dormant A-language", he said if the A-language is just in a passive dormant state, one might be able to "activate" it with a lot of hard work, but one absolutely needs a native speaker to correct one's mistake
That I do not have access to, unfortunately. and so I am improving my passive A, but not improving much on the active side, not as much as required......
are you planning to take any entrance exams next year, by some chance?