I would say if in doubt always go by what it says on the packet that the food comes in, if at all possible.
In the booklet you get in your folder they give you at meetings it said chicken was 4pp per 164g, the stuff I bought the other day was 4pp per 120g (or there abouts)
The way something is cooked, the weight, and the stuff added to it, can all change the amount of PP something is.
I go to Sainsburys (love there pie chart on the labels showing you how healthier the food is) I try to stick to foods with as much green in the pie chart as possible, that way I know its probably going to be less points then the same item of food with more red parts, its obvious to most but helps me.