The switch to carts is a near certainty. At that time, they would have been much more reliable than vinyl records. In fact, I own two carts of DS music cues I've bought at the festival auctions. I have played them at the radio station I used to work at. One cue was not used much, but the other is pretty familiar. Carts are similar to 8 tracks, but can only be played on special studio players. Although they were the standard for about 30 years, especially for commercials for example, few radio stations use them any more with the advent of digital audio formats such as Cds and MP3 formats.
Michael