Trevor Jackson's Playgroup guise produced dozens of remixes, singles, and DJ mixes, but only one proper full-length album. There were hours of unreleased tracks recorded during the years leading up to that album's release, and during the summer of 2016, Jackson released nine EPs (one per week between July and September) on a new label called Yes Wave Records. Released later in the year, the double CD Previously Unreleased collects most of the tracks from the series (many of which were co-produced by In Flagranti's Sasha Crnobrnja). Unlike the Playgroup album, most of these tracks don't feature guest vocalists, so they generally appear to be club tracks rather than proper songs. That doesn't mean this should be dismissed as a collection of inferior work or unfinished demos. The tracks are often simple, repetitive instrumentals, but they channel the best of '80s dance music, encompassing house, electro, Italo-disco, post-punk, and other styles, and they're always energetic and smartly assembled without being too sophisticated. Even the two tracks that stretch out to 12 minutes ("What's Happening?" and the more serene "Little Things," which features guitar by a young Kieran Hebden, aka Four Tet) have a steady, hypnotic flow to them and stay engaging. Plenty of tracks nail the early acid house sound, with tracks like "Move My Body" and "I Want to Believe" (featuring EDMX, aka DMX Krew) consisting of stripped-down rhythms and simple, commanding vocal samples. Other tracks venture into heavy dub territory, piling on crazy effects like Adrian Sherwood or Mark Stewart, but Jackson's dub excursions incorporate post-punk basslines or hypnotic beats closer to dub-techno crews like Basic Channel than any producer from Jamaica. The electro tracks are equally indebted to Kraftwerk as well as the hip-hop pioneers directly influenced by them. Only two songs have proper vocals, and they're both sung by Mike Z of Philadelphia minimal wave legends Crash Course in Science. Think of Previously Unreleased as the alternate history of Playgroup, and a fascinating treasure trove of unheard goodies.