You indicated that 20 cases have been undertaken.
I assume you receive complaints, look at them and in some cases say, “This simply can't be pursued,” or “This doesn't have merit,” or “The nature of the evidence provided is inadequate,” or something like that.
Twenty being the number of cases you've looked into, how many would you say have actually come in over that 20-year period? What proportion do you perceive...? I'll leave it to you to figure out the right way of giving an answer back to me.