Good point, Faldage. And the noun phrase functions as an adjective. You still should, I think, give a nod to how the words in the phrase are functioning. Titles, for instance: Much Ado About Nothing. There we have a pronoun functioning as an adjective, a noun, a preposition and a pronoun again functioning together as a noun--a very proper noun, in fact--but that doesn't change the fact that the words that make up the title still are what they are in terms of parts of speech.

Participles can be harder to nail down, but unless you have a case as you showed above, generally 'ing' forms of verbs that modify nouns are going to be participles and not gerunds. Grammarians today would classifying such 'ing' modifiers as present participles and not as gerunds. The case you have shown us is one of those glorious exceptions to the rule, such as it is. But to present the exception as the rule would be misleading. Generally, 'ing' forms of verbs modifying nouns will be participles functioning as adjectives--and then to have lots greater understanding of the flexibility of the language, pull out all those possible exceptions. This is the kind of exercise that I expect gives experts in linguistics papers to write. However, were I to teach my ninth graders that present participles modifying nouns were gerunds, I think I would be leading them astray.

If you want to fervently hold on to the belief that gerunds are adjectives, then I suggest that you begin a letter-writing campaign to the board members on AHD and suggest that they redefine 'gerund.' ('Letter-writing' here has been used as an adjective modifying campaign and not as a gerund.)