This business about proper nouns (or adjectives, or whatever) has been bugging me. If we take a proper noun as the name of a specific thing, so "John" identifies a particular person (albeit there being lots of Johns), then (say) "agapanthus" identifies a particular type of plant but does not individualise it, and therefore is not a proper noun (although it is tempting to capitalise it).
Collie is a breed of dog, but not a proper noun unless the dog happens to be called Collie.
Wales is a proper noun, because it uniquely identifies a specific country from the set of all countries (that are independent states...). However, a person from Wales belongs to set "Welsh", and is not uniquely identified by the adjective, therefore "Welsh" is not a 'proper adjective' (and by that token there is no such thing as a 'proper adjective'), despite it being spelt with a capital.
I get into more of a tangle with the likes of "Mondeo". Clearly this is commonly regarded as a proper noun, but it does not uniquely identify a specific individual car. Sigh.