I can think of three times while I was keeping my Top 40 charts that two versions of (more or less) the same song were in the countdown simultaneously. In late spring 77, Bill Conti and Maynard Ferguson scored with “Theme from ‘Rocky’.” Later in 77, Meco took on the London Symphony with the “’Star Wars’ Theme,” and then he did battle with John Williams on “Theme from ‘Close Encounters of the Third Kind’” early in 78.
I’ve learned in recent years of times earlier in the 70s when this phenomenon occurred. In early 74, “The Americans,” a spoken-word recording of an editorial written by Canadian journalist Gordon Sinclair, hit in versions by Sinclair and Bryan MacGregor (MacGregor’s reading was by far the bigger seller—go figure). There were three versions of “Theme from ‘Love Story’” on AT40 for four weeks in Feb-Mar 71 (two instrumentals, by Henry Mancini and Francis Lai, and one vocal, by Andy Williams).
And then there was the song adapted from a commercial for Coca-Cola (courtesy of Don Draper, right?). Starting with this show, the Hillside Singers (#26) and New Seekers (#28) went mano-a-mano for nine weeks. The Hillsiders had a head start, debuting the previous week, but the New Seekers won the war, peaking at #7, versus a high of #13 for their competitor. The NS version sounds more like what I remember of the ad, but the HS version definitely has its folky charm. You have to think that they hurt each other’s sales—would a single charting record have come close to #1? We’ll never know.
Can’t help but notice in writing this up that the multiple-version thing at that point in popular music appears to have been limited to movie themes and novelty-ish stuff.