Now that you mention it, it sounds kinda true. PBS is actually very helpful when comes to grading the overall grades

Most likely all three are low F and the A is also low.

I think they add up all papers and use the total marks to draw a new graph, hence resulting in different final grades despite same semester grades.

Your teachers have made an understatement there regarding your friend's result. Yes, we don't really know how MPM calculated her overall STPM grade, but only God knows how much of blood, sweat and tears she poured into her studies.