Being that written lyrics were allowed, and he was an established rapper, the idea is not far fetched. To opomize his time he would conjour up a few lines, then insert four to six lines of his own. Then continue as so.

In example, this rapper has two albums done. Each contains, on average, twelve songs. Each song has, also on average two verses contaning sixteen bars. (1 Bar = 4 Bines = 2 Rhymes)

With the knowledge of those songs in his mind, he still need be a great freestyler, but his ability to fall back on old material takes some of the flair away from it.

It was still a great effort, and note worthy.