I'm listening to a Canadian station play AT40 and they gave us Don Goodwin's This Is Your Song (1973) as an extra, right before #27, where I think other audiences probably got a true AT40 Extra. Nice one, and I assume it fulfilled the Canadian broadcasting requirement that a certain percentage of songs (30%) must be from the Great White North...
On the 11/28/70 replay heard today on KFRC SF, were the original extras as intro'd by Casey:
After #28, the #1 song from ten years earlier, Elvis' "Are You Lonesome Tonight"
After #15, a cut from the #1 album of the week, Santana "Oye Como Va"
After #9, a 60-sec promo ad for the Osmond's "One Bad Apple" (repeated after #2)
After #3, Dawn's "Knock Three Times," about to enter the Top 40 on its way to #1.