This has been one of the most well-known parts of the case for the past 17 years at least. Hunting a Predator, Sudden Terror, I'll Be Gone In the Dark all mentioned it repeatedly. Any of the TV documentaries - Cold Case Files, Golden State Killer - It's Not Over, Unmasking a Killer, they ALL feature Mary Hong talking about this scenario.
There were 49 EAR attacks.
Because the statute of limitations expired all DNA evidence was meant to have been thrown out - there is a limit to storage space and they can't simply store the thousands and thousands of pieces of evidence relating to crimes which can no longer be prosecuted.
Mary Hong found three duplicate kits in Contra Costa County - they were supposed to have been thrown out long before but had accidentally survived in storage. She was able to conclusively prove for the first time what the investigators had always known - that the same man had committed the three rapes in question.
There is no DNA evidence in any of the other 46 EAR cases, across all the jurisdictions.
The only three EAR attacks which DNA exists for are:
Attack 39 in San Ramon (October 28th 1978)
Attack 42 in Danville (December 9th 1978)
Attack 46 in Danville (November 6th 1979)
You will not find one link that will give you all this information, I have listed some of the many places you can find parts of the story above.