I'm not sure when 22 CFR § 126 was originally enacted, but it seems to be updated fairly promptly most times that a nation's embargo status changes. (Just out of curiosity, I may watch to see how soon the status of Cote d'Ivoire changes, as its UN arms embargo was lifted on April 28th of this year.)
Kuwait, Saudi Arabia, and Egypt are not, and have not been, subject to UN embargoes.
22 CFR § 126 restricts all arms imports "originating in certain countries" regardless of what other countries they pass through on the way, who is doing the importing, and how. However—although I'm no expert on ITAR—the main practical effect of the law as it relates to small arms imports is on corporations and FFL importers; a licensed importer or company striving to operate aboveboard is not going to risk illegally importing items that may originate in an embargoed country.
OTOH enforcement seems to be relatively lax as it relates to private citizens and servicemen returning from abroad with a souvenir firearm in their luggage, and I surmise this is how most firearm "unicorns" have wound up here. Also, I've been told by some knowledgeable milsurp enthusiasts that simple possession of a restricted ITAR import already within U.S. borders is not a crime, and my reading of the law seems to agree with this; 22 CFR § 127 clearly says it's a crime to export a restricted item, import or attempt to import such an item, or to facilitate the transfer of such an item from one foreign entity to another, but it does not appear to criminalize simple possession or transfer of the item within the United States. (This of course assumes that possession of the item is not illegal for some other reason, e.g. a firearm with the serial number defaced.)