Difference between OS and STOS

What is difference an OS and an OS Specially Trained? Came up on Northwest Sailor YouTube cha.

The definition that I have always operated with is that an STOS can steer. It is essentially an AB limited but a way for companies to get away with paying OS wages.

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From Volume III of the Marine Safety Manual, Page B2-3:
A specially trained ordinary seaman may be substituted for able seaman in certain situations. If an ordinary seaman receives additional lookout procedure training, it is within the discretion of the local OCMI to allow the substitution of an able seaman with a specially trained ordinary seaman…

If the vessel is subject to STCW, it’s an OS who holds an STCW endorsement as Rating Forming Part of a Navigational Watch.

Steering is probably not relevant, as anyone with less than AB cannot be on the wheel “in ports, harbors, and other waters subject to congested vessel traffic, or under conditions of reduced visibility, adverse weather, or other hazardous circumstances.” See 46 US Code 8702(d). This restriction is why the vessels I worked on were allowed to carry 2 STOS, but never did.

Yes that’s what video said. Also said that you needed to take initiative to upgrade on your own by doing extra watches, if your captain lets you, or take classes.