Thank you Zed Nocear, sorry for the delay I'll add it to the tutorial.
Further, there have been findings that ADD_GAM_NPC is not a good idea to use at all:
ADD_GAM_NPC and uninstallation, non-functionality of .
So it seems that ADD_GAM_NPC, since it changes save-games, screws up the whole BG1 game, if the mod gets installed more than once. Since it is possible that a mod gets installed and deinstalled in one game installation (e.g. if the player decides to change the order of mods), this would lead to a malfunctioning NPC-creation (multiple times) if coded using ADD_GAM_NPC. Thank you Miloch and Red Carnelian for pointing this out!
I'll add the link and a comment in the tutorial that ADD_GAM_NPC is not recommended.
EDIT: Tutorial is updated concerning 107 MoveToOffset(P:Offset*) and ADD_GAM_NPC.