one thing ive noticed on a lot of colorsets are a full color scale, and then duplicates of said color scale in different tints/saturations/etc
honestly, such duplicates are rarely useful. if you try to build with them you'll notice you'll default to one row when it comes to using primaries. softs are an exception (lightly saturated) but you rarely need similar softs (see the third last and second last color in the first row)
the best colorsets tend to come after weeks of testing through building with it. you'll find you'll want certain colors depending on the situation, and sequentially adding these special colors develops your colorset fairly well. Trueno's colorset specials are a good example, while emil's colorset and architectural revised are basically 70-80% specially chosen colors.