I am aware of people who have gotten temporary permits to go to Cuba. They did it on COIs for only 20 miles offshore routes, and with Near Coastal licenses and no STCW. I don’t know what the legal basis was, but the USCG specifically permitted it.
I am aware of boats in the US Virgin Islands that routinely go back and forth to to the BVIs. The six-pack boats have to get BVI inspection (they get 12 paasengers). They do it on Near coastal licenses without any STCW. I believe the US/BVI have an MOU that covers that. It use to be similar in the Bahamas.
A lot of the STCW countries have inspection requirements and Master’s license requirements for “commercial yachts” - crewed charter or daysail. Other countries do not have uninspected 6-passenger boats like the US.