[PF] Monster Class Levels and Ability Scores?

[ClockworkSun]

I'm starting up a new campaign, planning to use derros as the first group of enemies for the PCs to fight. I want to include a boss derro with class levels, but I can't figure out how to go about creating its stats. The derros in the Bestiary have a certain set of stats (Str 11, Dex 15, Con 18, Int 10, Wis 5, Cha 16), but a different set of stats for a 6th level derro sorcerer exists in the Classic Horrors Revisited book (Str 9, Dex 18, Con 18, Int 14, Wis 5, Cha 22, no stat-boosting items). Is there a good way to reverse-engineer these ability scores to figure out what racial adjustments I'm looking at here? I'm also guessing that the plain derro has normal NPC distribution of stats, but the sorcerer has the heroic NPC distribution.

[Urpriest]

I don't know how much of this applies to PF, but in 3.5 you'd say that the derro has Dex +4, Con +8, Wis -6, Cha +6. The sorceror would then have base stats Str 9, Dex 14, Con 10, Int 14, Wis 11, Cha 16. That doesn't jive with D&D's distribution of elite NPC stats, but it might jive with PF's. Does it?

[ClockworkSun]

That sounds about right, and for reference:
Basic: 13, 12, 11, 10, 9, 8
Heroic: 15, 14, 13, 12, 10, 8

The +/-6 for Cha/Wis definitely makes sense, as a wish or miracle to cure a derro's madness negates those scores. I have no idea how much the Bestiary races were built off the NPC scores given in the Core book, but they seem appropriate at least for humanoids.