Cover mounted free cassettes were common and popular,
until the CD was invented,
and in some cases for a longish time ater..
Early 80s NME casettes have gone down in cultural history,
they were such important compilations...

"Between 1981 and 1988, the venerable British music magazine NME released a staggering thirty-six cassette compilations. These were created as giveaways, intended to be promotional items rather than artifacts of lasting cultural value. Somewhere along the line, though, the C81 and C86 tapes became part of the unofficial indie-rock canon. "