Please introduce the check into AR9800.BCS for Tilorn appearance. It is a single GLOBAL which checks whether it is BG1 or BG2.
Ulcaster school is AR9799, not AR9800. So it should look like this, then?
IF
OnCreation()
Global("VP_Create_Tilorn","AR9799",0)
Global("ENDOFBG1","GLOBAL",1)THEN
RESPONSE #100
SetGlobal("VP_Create_Tilorn","AR9799",1)
CreateCreature("TILORNN",[236.2918],0) // ~Tilorn~
END
IF
GlobalLT("VP_Hrothgar_Tilorn","GLOBAL",
Global("ENDOFBG1","GLOBAL",1)THEN
RESPONSE #100
SetGlobal("VP_Hrothgar_Tilorn","GLOBAL",

ClearAllActions()
StartCutSceneMode()
StartCutScene("VPCutH06")
END
IF
GlobalGT("VP_Leaving_Halruaa","GLOBAL",4)
Global("VP_Create_Orcs","AR9799",0)
Global("ENDOFBG1","GLOBAL",1)THEN
RESPONSE #100
SetGlobal("VP_Create_Orcs","AR9799",1)
CreateCreature("DarOrc1",[3259.643],3) // ~Orc Bandit~
CreateCreature("DarOrc2",[3328.582],3) // ~Orc Bandit~
CreateCreature("DarOrc3",[3351.639],3) // ~Orc Bandit~
END