Are they talking about “Top 40” hits, such as on the Casey Kasem countdowns, of big hit songs, as opposed to album sales, or how do we define these?
They note a hit song by Charley Pride, who I think had a number of country big hit songs, but perhaps just this one made a splash on the “Top 40” music charts.
If they flipped it, and had artists with only one country hit in the ‘70s, they could include Paul McCartney, who hit the country charts with Sally G (flip side of Junior’s Farm)