In Wizardry 6, are spell effects for party buffs or enemy de-buffs cumulative? For example, if three characters all cast "Bless," is the effect the cumulative of all 3? And if three all cast "Weaken," do the monsters experience a cumulative weakness from the spells?

So does that mean that, not considering variation due to character level, stat.'s, and general randomness, two characters casting a Lv. 3 Bless would be equivalent to one character casting it at Lv. 6? And that if one character casted it at Lv. 6, there would be no additional benefit from anyone casting an additional such spell?
Also, is there any way to know how long the effects of such a spell are in place? It seems like this is only the case for the few spells that have dedicated icons on the screen (Enchanted Blade, ArmorPlate, etc.).