Do you really need me to explain this to you? Say the actual, absolute rate of something is 1 in 150. However, because it is not well understood the rate at which it is recognized is 1 in 300. The "perceived rate" would be 1 in 300, while the absolute is still 1 in 150. If it suddenly gets recognized better due to improvements in diagnoses, the "perceived rate" may increase to 1 in 200. Does this mean that the rate has increased? No. It is still 1 in 150, but the perception will be that it increased. Is that so hard?
If you are not part of the solution, you are part of the precipitate.