How can I identify an AD as being a State of Design AD?
In principle, an AD is a State of Design AD when the authority that issues the AD is, on the date of issuance of that AD, the State of Design authority for the products, parts or appliances (or STC modification) to which the AD applies. The Type Certificates of some products have been known to move from one State of Design to another in the recent past, e.g. the Bell 206 and 222 helicopter types moving to Bell Helicopter Textron Canada, from the USA to Canada; the British Aerospace 125 business jet type design was sold to Raytheon (now Textron Aviation, Inc.), moving from the UK to the USA; and APEX sold the R 2000 type design to Alpha Aviation, moving the State of Design (responsibilities) from France to New Zealand.
When operating a product for which France is the State of Design, e.g. an Airbus aeroplane, or a SAFRAN helicopter engine (formerly known as Turboméca), the applicable ADs are those issued (or approved) by EASA and, previously, ADs issued by DGAC France.
When operating a product for which the USA is the State of Design, e.g. a Boeing aeroplane, or a General Electric engine, the applicable ADs are those issued by the Federal Aviation Administration (FAA).
When operating a Bell 206 helicopter, the applicable ADs are those issued by the FAA before 14 September 1995, and those issued by Transport Canada Civil Aviation (TCCA) after that Type Certificate transfer date. The TCDS EASA.IM.R.512 contains lists (for each Model) of valid pre-transfer FAA ADs.