Positive and negative feedback is not valid forever. After a period of 30 days, each feedback (positive or negative) gets a smaller and smaller weight. That means it gradually loses its impact on your overall score. After about 60 days feedback will only have a very small influence on your overall score.
If you see very big jumps in your feedback percentages, this may be due to negative feedback fading out and positive feedback being added (and vice versa).