Agreed. I'm not a law student at all and I'd like to think that I'd know better.
What's the difference, in this case, between the 2005 law and the 1995 law?
I don't know the exact details - other than the 2005 law has a broader definition of things than the 1995 law (e.g., what AJHawkFan already said is correct).
As a side-bar:
It's a well-known fact that Tom Corbett and Graham Spanier HATE each other, and that goes back prior to 2011. They feuded a lot as regards how much Harrisburg funded Penn State.
Which is fine, but I tend to think that Corbett, a very powerful Republican in Pennsylvania politics and Governor for a time, had a strong influence in terms of the AG deciding to try Spanier under the 2005 law as opposed to the 1995 law.
Corbett was your typical "politician with a vendetta" in that regard - he had to have known that prosecuting under the 2005 law was wrong but "damn the rules, arm the torpedoes, I have a score to settle."
Again, I don't love Spanier - but the above isn't right either. Paterno acolytes or anybody else who points that out isn't wrong.
Then on another side-bar: there's the fact that the PA Attorney General has gone from Republican -> Democrat -> Republican from 2011 to 2019. The 2 Republican AGs were more aggressive vs. Spanier than the 1 Democrat.
In fact, that 1 Democrat (Kathleen Kane) was, for a very brief period of time, considered the "great white somewhat-attractive-for-a-50-year-old brunette hope" among many Paterno acolytes because of the fact that she was very combative against Corbett.
But then Kane shot herself in the foot in terms of future influence because of something ELSE: orchestrating a public release of confidential grand jury evidence! She's now completely disbarred - AND in prison!
Good old Pennsylvania politics.