I went through this with them explicitly about 6 mos ago. In acknowledging that the newer injectors flowed about 608, rather than a true 615 they downplayed the differential from 555. Its certainly possible I misunderstood, but the message I got was that their settings are "good enough" since the difference is not that great, and one size fits all anyway. In a sense that is correct when dealing with generic tunes, since every setup is going to be a bit different.