In PerfectIt I noticed there are two versions of my style, one with (Old) next to it. What is the difference between these two versions?

When we release a major PerfectIt upgrade (e.g., from version 3 to version 4), PerfectIt makes sure you keep your old styles. PerfectIt imports them into the new version and adds the ending "(old)" so you have both your previous version as well as a new one that contains any updates we've added.