A permanent and total disability rating under the provisions of §§ 4.15, 4.16 and 4.17 will not be precluded by reason of the coexistence of misconduct disability when:

(a) A veteran, regardless of employment status, also has innocently acquired 100 percent disability, or

(b) Where unemployable, the veteran has other disabilities innocently acquired which meet the percentage requirements of §§ 4.16 and 4.17 and would render, in the judgment of the rating agency, the average person unable to secure or follow a substantially gainful occupation.