Am I exempt from 36 months of obligated service to pin on SFC?

I am currently a SSG (E6) in the Army National Guard. Prior to joining the National Guard I was a Gunnery Sergeant (E7) in the Marine Corps Reserve. I have been selected for SFC (E7) and my unit is requiring me to extend for 36 months to have the required amount of obligated service to pin on SFC. AR 600-8-19 dealing specifically with National Guard promotions states this:

7–8. Service remaining obligation

a. The following service remaining obligations, from effective date of promotion, are required for promotion to SGT through SGM:

(2) To SFC through SGM, 36 months.
b. Service will be obligated from the effective date of promotion and Soldiers must extend within 90 days to meet the above requirements. However, Soldiers are exempt from this requirement if they are—
(1) Eligible through prior service for higher grade at time of retirement.

My question is am I required to be obligated for 36 additional months since I am already eligible to retire at the pay grade of E7 due to the fact that I have over 36 months of service as a Gunnery Sergeant in Marine Corps Reserve? I believe I am exempt from the 36 months of additional obligated service because I have already served 36 months as an E7 in the Marine Corps Reserve.