Photo of a 50 year old Glasspar transom, what's a good test?

I got a couple hours of grinding in today and the hull side of the CSM on my stringers appears very intact...only a few bad spots. How far down should I go or will I be ok laminating the 12oz 45/45 onto these areas with epoxy? It seems redundant to grind these large areas down to the roving of the hull when they appear to be as one. I've feathered the original CSM as carefully as I could. Forgive my ignorance. I've read so many posts about grinding but all I can extract from them is that the idea is to create sound, smooth transitions for new glass to bind to without damaging the hull.