How can I determine if someone is authorized to wear the SSI MOHC from our former unit?

CW2 (Join to see) - That is a milper for the Expansion of Global War on Terrorism Expeditionary Medal Area of Eligibility for Operation ENDURING FREEDOM.
For example it lists about 56 countries now eligible for GWOT-EM for support of OEF/OIF/OND/OFS/OES.
Only 28 of those countries are/were eligible for IDP.
Of those 28, only 9 are/were also CZTE, meeting the AR 670-1 requirement of "for Soldiers deployed to the USCENTCOM area of operations in support of OEF who received combat zone tax exclusion and hostile fire/IDP as identified by USCENTCOM Command Center–Joint Staff for Personnel and Administration."

I'll use Kuwait again as the example: Kuwait has been in the AOE for GWOT-EM since the beginning, but it hasn't met all the criteria for an SSI since 1993 and the end of DESERT STORM.

From whom did your former Soldier receive this information/ guidance that they're now authorized to wear the SSI MOHC?

ack'd and tracking all. Their leadership, based on the " Soldiers who were deployed in the area of operations on training exercises or in support of operations other than OFS are not authorized the SSI-MOHC, unless those exercises or operations became combat or support missions to OFS." and the stipulation that it doesn't mention specifically mention the czte stipulation if it's for training or ISO. I appreciate all the feedback. I concur with you as well, I've heard of stranger approvals and or auth to wear figured I'd get on here to see how it was justified.

CW2 (Join to see) - I would venture to guess that of the "approvals or auth to wear" you have heard, that the stranger they seemed, the more likely they were personal justifications or misunderstandings, and not an actual authorization meeting the three criteria listed in the reg.

And the misunderstandings are rampant, literally millions of Soldiers had one or more deployments that met all but one criteria over the last 23 years.
But a lot of those also had one or more deployments that did meet all criteria.