Not much doubt this is an Ambassador; the question is, how do we catagorize it? Medallion case back with serial number starting with "1 - " as well as clamshell say it's an International model. Every 30 jewel Ambassador in the database has a variation of this unique back as well as a similar s/n.and we have no ads for this configuration (30 jewel).
My thoughts are that 30 Jewel Ambassadors were all produced in Europe for the Non-US market.; hence, no ads in US publications. Face on this one is marked Swiss, and the 30 jewel movements for US watches were all US "in house" produced , and the top of the line. Face marking suggests movement was produced in Switzerland.
Case back is dated N2, which matches box style (which I have never seen in green or marked as this one is.) Watch is an open through the crystal and I'm not confident enough to open it up.
My thoughts are that similar Ambassadors with a 30 jewel movement and European style serial number should be called out as either "Ambassador - International (variant)" or "International - Ambassador (variant)". It seems they should get their own sub-catagory and be grouped together until we determine if they had European advertised variant letters.
"International Line" vs. "International LTD" also comes into play. Ad referenced is way off by date (1965 vs. 1972) but at least helps confirm the premise for my theory.