Wow, I don't understand this logic one bit. Historical sexual assault cases are prosecuted quite often, even though no rape kits were collected, and so forth. But this whole idea that more cases make a claim less credible is nothing short of ludicrous to me.
Imagine a case (and there have been many) where, say, a physician, a teacher, or a priest -- people who have some power, authority, wealth, or prestige -- is accused by several people of some sort of sexual abuse or misconduct years after the event. Do you honestly think that the police or prosecutors are going to think something like:
"Hm...well, too bad that there are so many people making allegations. If it was only one or two people, I think we'd take them seriously. But I can't believe that Father/Doctor/Celebrity X is the kind of guy to do something like this so many times. After all, there is no evidence of rapists or sexual abusers as being serial offenders."
You're moving the goalposts as well with discussing 'irrefutable evidence'. Historical cases are prosecuted successfully all the time, without the benefit of things like rape kits. Here are some recent examples from the region where I work:
http://www.cbc.ca/news/canada/north...ced-to-19-years-for-child-sex-abuse-1.2943720
http://www.cbc.ca/news/canada/north...o-to-trial-on-sex-charges-august-10-1.2944736
Without the benefit of rape kits and other circumstantial evidence, would you really rather such potential offenders go without prosecution or punishment? I wouldn't want to live in that world.