What’s the difference between Pain and Suffering and “ additional”..?

Basically APSC is:

The APSC is payable to a Veteran who suffers from one or more disabilities:
that are creating a permanent and severe impairment;
that are creating a barrier to re-establishment in civilian life; and
for which the Veteran has been granted a Disability Award, Pain and Suffering Compensation, or a Disability Pension.

APSC link: https://www.veterans.gc.ca/eng/about-vac/legislation-policies/policies/document/2828

PSC Link: https://www.veterans.gc.ca/eng/about-vac/legislation-policies/policies/document/2826

Im trying to figure out what differentiates a veteran who has “ pain and suffering “ , and one who has “ additional pain and suffering “? What dictates the add on, is it the type of injuries, the % or something else.?