When Tommasini first introduced the SLX model, it was called Prestige, along with one of the SL models. Based on the combination of a bridgeless bottom bracket shell and internal brake cables, I have no reason to doubt the tubing decal. You are correct, it was Tommasini practice to locate the tubing decal near the base of the seat tube on the smaller frame sizes. Tommasini's terminology for the fishnet finish was retinato. Based on the combination of frame features and the SLX decal in combination with the SL decal of the fork, it should be circa 1985-1987.