1998 Grady Adventure 208

I believe it was 1997 when they started making the transition from plywood to Greenboard XL.
 
I have a 1999. It's transom is definitely wood, but has held up fine!
There's a difference between the two materials used though. I believe everything before 1997 used marine grade plywood that can and very oftentimes does collect moisture/water and will rot quite badly. In, again I believe it was 1997, Grady White switched over to using Greenwood XL and it's supposedly much better at resisting the rotting. Although some obviously still do rot.