Starting about 20-25 years from now, these kind of situations regarding claims going way back into the past will get a heck of lot easier to investigate.
The prevalence of smart phones today, life today involves frequent selfies, WhatsApp chatting, snapshat, posting on twitter, Instagram, Facebook. My own teenagers today rarely take a piss without chatting about it (or during it). Some guy 30 years from now trying to maybe get nominated for the Supreme court, who was in high school in say the 2000's, if he was truly at some party involving some number of other teenagers, he probably wouldn't be able to get away with denying he was there or knew somebody etc. There will likely be at least some electronic information out there for the FBI sift through when doing background checks like old WhatsApp messages, Instagram, Facebook posts.
In a crude way, it is what Kavanaugh has being trying to do with his calendar books. Saying, 'hey look, here is what I was doing on weekends during summer X'. But 30 years from now, the Kavanaugh type of person won't have been keeping any calendar books. He'd have had his iPhone. And much of that will have been electronically documented in some fashion via his smartphone and the smartphones of anyone he hung around with. I guess you can try to purge everything you can if you are trying to go through some kind of process like this, but some of it no matter what you do will just be out there forever in the cloud.
But in this current case, since we are talking about high school in the early 1980's, all we mostly got to go off of in something like this is stuff like calendar books written in crayon and pen and people's statements regarding their memories (or claims of or lack of memories).