Chris:
A "Green Card" is nothing more than a standardized presentation of proof of insurance coverage for one or more countries.
If a vehicle is insured for operation in one country only, the insurer can issue a certificate of insurance that is recognized in that country only. Examples of this can be seen on the link I posted above about individual country insurance policies in the Balkan countries.
If an insurer issues an insurance policy valid in more than one European, North African, or Middle Eastern country (or any combination), they will provide proof of insurance coverage in a document that is compliant with
COB (Council of Bureaux) specifications. This document specification has been in use since the early 1950s. The COB has since come up with
other protocols to enable recognition of insurance issued by various countries, but the Green Card format is still in use and has not been deprecated by these newer protocols.
What needs to be understood here is that the Green Card is only a document specification. Hence, it is up to each individual insurer to make their own determination of what countries they wish to provide coverage in. An insurer may offer the purchaser choices - for example, they may offer their customer coverage in only the Western European countries, or in Western Europe plus any combination of additional countries in which the insurer is authorized to underwrite insurance coverage.
Participants come to the HUBB forum to gather accurate and up to date information prior to international travel. We who participate in the forum need to take care that we do not provide misleading or inaccurate information in the post that we make.
To suggest that coverage is "automatic" in any given country is misleading and inaccurate. The geographic extent of insurance coverage provided is a private commercial decision between the person purchasing the insurance and the insurance company providing the coverage. The insurer may choose to only offer coverage in certain specific countries, and likewise, the purchaser may choose to only purchase coverage in countries (or country groups) that they intend to operate their vehicle in.
The only thing that a "Green Card" guarantees is that it (the document) will be accepted as proof of having the minimum legally required coverage to operate the vehicle in countries whose code is not crossed out by an X on the document.
Your comments about whether or not one is a Canadian (or other person foreign to the Green Card region) or not, or whether the vehicle is Canadian (or otherwise foreign to the Green Card region) are not relevant at all. At the same time in the past that I was riding my Canadian plated motorcycle in Europe and had a Green Card to show that the motorcycle was insured in Europe, I was living and working in Switzerland and driving a Swiss plated car. I also had a Green Card for that car showing that it was insured for operation in various European countries.
TL;DR - The Green Card is nothing more than a standardized presentation of a proof of insurance document. Check the document to see which countries it shows you are insured in. Don't make assumptions, and don't take anything for granted.
Michael