code: def __validate_enrollment_periods(self, enrollments):
          
  
          for a, b in itertools.combinations(enrollments, 2):
  
              max_start = max(a.start, b.start)
              min_end = min(a.end, b.end)
  
              if max_start < min_end:
                  msg = "invalid GrimoireLab enrollment dates. " \
                        "Organization dates overlap."
                  raise InvalidFormatError(cause=msg)
  
          return enrollments
docs: Check for overlapped periods in the enrollments