Speaking just to this point …
The statute of limitations is a recognition that the outcome of the legal system is based on fallible human testimony. And on perishable evidence.
The quality of both those things deteriorates over time. And after enough time passes, the quality is so low that the outcome of any trial would be little more valid than spinning a wheel of fortune.
e.g. I’m nobody famous. Say tomorrow I get a court summons saying somebody is alleging that I date-raped them in college back in 1978. Or that I was the guy who stuck up their liquor store on October 27th 2001.
So now we’re going to have a criminal trial where I’m the guest of honor. How likely is it that reliable witnesses will produce reliable testimony? Even if they fail to convict me, I still get dragged through the system, need to pay for my defense, have my reputation trashed, etc. And the taxpayers gets to pay for the court, the prosecutors, the detectives, etc. Lots of resources are consumed all around. To what good end?
In many cases even proving that something happened to the complainant on that particular day would be difficult, much less that the specific person now on trial was the one who did it.
There comes a point where the probable benefit to society is less than the probable cost. Remembering that one of the guiding tenets of our justice system is that it’s better to let the guilty go free than to imprison the innocent.
As you yourself say: “Now we can never really find out the truth of these allegations”. But the reason we can’t isn’t the lack of a trial now; it’s the passage of time. A trial now might create a lot of testimony, but the testimony’s connection to the actual truth of an incident 20 years ago would be slim at best.
The saying “Justice delayed is justice denied” applies both ways. Neither victims nor defendants get a good result years later.
Turning more towards the specifics of this case, it’d be a damn shame if indeed there were crimes that weren’t prosecuted when fresh due to celebrity immunity. Immunity, also spelled impunity, is one of the most corrosive cancers in a legal system or in a society.
OTOH, if the reason they weren’t prosecuted when the crime was fresh was that the injured party wanted to ignore the whole thing, well they don’t get a do-over umpteen years later. And they knew, or should have known, that back then when the allegations were fresh.