@IH82BL8 , I've taken all the covers off the cushions on my '84 H31. The covers look replaced but I'm fairly confident the foam is (was) still original. In my case it was the same as you describe: batting on the cushions at the dinette, but no batting on any other cushion (v-berth, port settee, and aft quarter-berth).
Fwiw, the thickness of our original foam was 3.5" throughout.
Also fwiw, if you ever decide to replace the foam in the seat cushions I would use 50lb ILD for seat cushions, not the 35lb. With 35lb I found I just sank down to the wood. Also, when I put new 50lb ILD foam in our seat cushions without the batting our old covers got wrinkles in the top, but it didn't do that on the other cushions that didn't have batting originally.
A little off topic, I replaced the foam in the V-berth ('cus that's where my wife and I generally sleep). I purchased the foam from foambymail.com (aka thefoamfactory.com) and the results are extremely comfortable to my wife and I.
I posted more info about our v-berth mattress here:
https://forums.sailboatowners.com/index.php?threads/interior-cushions-mattresses.189379/page-2
