Mickey Walker is the founder of SPA and he is the one who approves models for use in SPA contests. He made a decision some years ago that grandfathers in variations of a basic design, regardless of when the variations came about. Hence the approval for the derivatives of the original Kaos design, the Phoenix series, and the LFX series to name a few. One of the issues that this addressed was availability with the Phoenix 7 ARF and the large number of Kaos inspired designs (Killer, Utter, etc.) Yes, there are some strange consequences such as having the P8 on the list as you point out. But at least there is a little bit of a rationale for what has been done.

Jeff