What regulations or policies cover the Overseas Service Stripe (Combat Stripe)?

Yes, it is

Qualification for the US Army overseas service bars is covered by AR 670-1.
Basic qualification is for six months in a designated service area; with, if memory serves, any time served in the first and last month counting as a full month for qualification. Also, if memory serves, shorter periods of deployment, to qualified areas may be combined to meet the six month rule.
http://ar670.com/articles/view/28/overseas-service-bars/296

From the information provided, you/your unit did not do a 12 month deployment, you did a 12 month activation.
Here is a short version of how this works:
Unit activated for a period of 6 months, 2 months of preparation and 4 months of creditable service. No Overseas Stripe, credit for 4 months.
Unit activated for a period of 8 months, 2 months of preparation and 6 months of creditable service. One (1) Overseas Stripe, credit for 6 months.

Example of 6 months of creditable service:
Month 1 - 1 day (also creditable for Combat Pay/Overseas Pay, etc.)
Month 2 - 30 days
Month 3 - 31 days
Month 4 - 31 days
Month 5 - 28 days
Month 6 - 15 days

In this example, though the actual length of time is less than 5 months, however due to the period covered 6 months is credited for the Overseas Stripe.
Hope this helps you understand.

SSG Robert Webster - Thank you for the response. I have been out for many years but have a function that I am wearing the uniform too and don't want to wear the incorrect number of stripes. So it sounds like in my case it's one stripe because we were boots on the ground 10 months even though we were activated for 12.

SPC Gabriel Botero Jr., MSW, LCSW - You got it.