The question is hard to answer because we don't possess logistics lists for the Roman army, and even if we did, we're not sure how they called LS. Lorica segmentata is the name given to it by historians. We can only extrapolate from archeological finds and pictorial evidence, both with their own pitfalls. If we find more LS than chainmail at a given dig site, it does not necessarily mean that LS was used more often, merely that it was discarded more often. As pictorial evidence we have Trajan's column, which shows all legionaries wearing LS; but the Adamclissi meteopes (which depict the same campaign) also has chainmail-clad legionaries. At best, one can conclude that the artists working on the column thought LS to be the stereotypical legionary armour.