Sega Music Networks published a magazine related to the Prologue 21 for a time. Exact publication dates are unknown, but I have obtained several issues from mid-1996 through mid-1998. I assume these magazines were meant to be available reading and informational material at select venues the karaoke machines would be at. The earliest one I have, Volume 3 from May 1996, includes what appears to be a full list of currently available songs (roughly 11,000) taking up the majority of the magazine. Most of the magazines primarily consist of band interviews, showcasing upcoming features, and listing current popular songs according to various metrics.
SEGA Prologue 21 