The purpose of the Red Books is it lists every advertising writer/producer in the business, what their campaigns are, what markets, etc. When marketing to an advertising agency you really need to submit to an individual for the best results. I've seen actors do mass mailings to advertising agencies with no "go to" contact person. Those will get thrown in the trash for the most part. Just like if you send your demo to an agent with a cover letter starting with, "To whom it may concern." Very impersonal and will most likely not get listened to. It's very easy to find out who the
VO agents are. Just like it's easy to find out who the ad execs are. Most free listings don't have the details that the Red Books have. It's over a thousand dollars to subscribe. But if you get one national campaign from your submissions, that will more than pay for your lifetime of marketing.
A good rule in marketing is to be specific. Know who you are marketing to. Know their territories. Know their demographics.