To the best of my knowledge, the SLX and SPX decals were available right from the introduction of the SLX and SPX tubesets. They appear in very early 1985 advertising copy and road tests. Given the time lag for writing, lay-up, printing and distribution of periodicals, these decals would have been available in late 1984. What you may be recalling are the SL frames with the SLX seat tube, as this preceded the SLX tubesets and such frames used the generic decal. The only instances where I could envison SLX frames with generic decals would be on pre-production test bicycle, possibly early trade show models and somebody putting on the wrong decal.