pr.probability – Probability of all “fails” being same individual

I’ve searched but am unsure how to go about working this out:

There are 100 members of staff who are all assessed annually. There are 5 assessment areas per person. Each assessment area has grading: A, B, C, D. Grades A or B are required to “pass”, C and D are “fail”.

100 staff were assessed by the same management, 99 staff achieved an A in all 5 areas. 1 staff member received 3 assessments of C. As the areas are equally weighted, that staff member then had 60% C rating and was therefore overall rated C – and failed.

What is the likelihood that of the 100 staff, all assessed on 5 areas with 4 grades in each:

what is the likelihood that of the 500 assessments (100 staff x 5 areas), there were only 3 which were not A

what is the probability that 100% of that number were all the same person