Avoid using definitives. Just because you won't remember, doesn't mean no one will remember. Someone will remember these ads. I still remember the first Destiny live action one, the "Immigrant Song" one...even though it's been longer than "6 months." Especially if I hear the song. Literally evertime I hear the song or something about Led Zeppelin, I think of Destiny. And sure people remember the Halo 3 ads even though the didn't have songs...but they had a slogan, "Believe." (Remember how I said jingles, songs, and slogans play a role in ads?) I can hear that word and remember that old ad campaign. Nostalgia also helps that...many fond memories of Halo 3. Whether you like it or not. Destiny's Led Zeppelin ads work. Psychology is fun, isn't it?