is it true the piece must always ALWAYS be a tad bit longer on the edges of the sides and back of the piece? Some stylists swear it must always be like that for the blending with thinning shears, but I have a piece now that was not cut that way and the blend is still very good.

You’re right--it does not ALWAYS have to be a tad bit long on the edges and the back of the piece. Sometimes stylists come up with stuff that is outside the scope of their normal work and this is one of those times.
John