Per the GMG:
For a creature that can cast as many spells as a PC spellcaster, the highest spell level the creature can cast is half its level rounded up. It gets five cantrips. If the creature’s level is odd, it gets two spell slots of the highest spell level (plus three spell slots of each lower level), or three spell slots of that level (plus four spell slots of each lower level). If its level is even, it gets three spell slots of the highest spell level (plus three spell slots of each lower level), or four spell slots of that level (plus four spell slots of each lower level).
So... what ultimately dictates whether they get 3-4-4-4-etc, or 2-3-3-3-etc? The odd/even level makes sense to dictate whether you get 2/3 or 3/4 of the highest level the monster/npc can cast.
Am I missing something? Is there some paragraph that clearly explained which set is chosen? At first I thought it might be Spontaneous vs Prepared casters (Spont. being 2/3-3-3-etc, and Prep. being 3/4-4-4-etc), but that doesn't seem to hold water when I take a gander at other NPC stat blocks.
In fact, even in the GMG it doesn't follow the "rules" or "guidlines". Take a look at Zealot of Asmodeous on pg. 213:
Divine Prepared Spells DC 19, attack +11; 2nd harm (×3), restoration, see invisibility, shield other; 1st detect alignment, magic weapon, spirit link; Cantrips (2nd) detect magic, divine lance, forbidding ward, read aura, sigil
That's 6-3-5! Nowhere close to what is recommended.
Priest of Pharasma is a tiny bit closer as far as Prepared Casters go, but still far off the mark:
Divine Prepared Spells DC 24, attack +16; 3rd circle of protection, heal (×3), searing light (×2); 2nd gentle repose, silence, spiritual weapon; 1st disrupting weapons, mindlink, spirit link; Cantrips (3rd) detect magic, disrupt undead, light, read aura, shield
That's 6-3-3-5, but still nowhere close to the build rules (unless, hopefully, missing something).
Any help here?
I think you forget the divine font
It probably makes not much sense to list it extra since it just gives a few charges of either heal or harm
beyond that the monster creation rules say themselves that it's mostly guidleines and you can ultimately tweak all the numbers however you want
Yep, Divine Font.
Also, Extra Cantrips, likely to give them more utility for a broader range of story purposes.
The GMG NPCs seem built with PC classes in mind, even if in many cases the NPCs are mix-and-matching abilities from different classes. High attack ratings would be the most obvious, yet there are others. Again, so the NPCs can suit different story purposes, yet also perhaps to adjust better in published adventures to who knows whom they might fight. These NPCs are ready for a spectrum of different PC powers and power levels, yet "too" ready for use as a PC.