Ex-Recruiter, and I'm assuming the employability score is what used to be called the group score; if so, it's a score made up of weighted scores from all the stanines. Technical trades will put more weighting on EC and MC, Admin on things like VR. However, all stanines are counted in some way, so electrical and mechanical scores still go towards Admin trades. Stanines aren't a direct number from your result; a 4 in WR could mean you got 12 out of 18 right, a 4 in NR could mean 15 out of 20 right, for example. All the scores are all done on computer, so no-one is going to know them off the top of their head and explain it to you.
Did you mean you reached/exceeded the stanine scores for the areas required for your trade? If so, but you scored low in other areas, you won't reach your employability score.
Eg, if you needed VR5, NR4, WR3 and employability score of 4 for your role, and got VR6, NR5, WR3 and an overall 3, it means you didn't do well in the other sections.
To improve your score requires you to do well in all areas of the test, do look at those with the lower stanines.