I've no idea if and how the Slazenger codes work, but it's clearly not related to the Wilson codes as that would be three different years!
After a bit of research, and seeing the similar Challenge Pro in the Slazenger thread, I can confirm a 1992-93 release date for this Plus model with listings through to at least 1995. It was quite a concentrated mid-range selection of at least Challenge 2000, Graphite, Pro, Plus, Comp, Demon (!), 1500, 1400, 1200, Match, Gold, Lady and Junior. From £40 to £80 in the UK, when the top of the range Mystiques, Phantoms and Silhouettes were £100-140. The Challenge 2000 was probably the only one you'd see in tennis shops, with the others in good department stores or mail-order catalogues. The 'non-PWS' OMS (Optimal Mass System) debuted in the 1988 Silhouette and Phantom and I believe it's a metal infused rubber, so mass and dampening is provided.