When I posted this I was speaking from personal experience, not being critical . The second anvil I acquired in the early 90s was a 125 pound Peter Wright in good usable shape as purchase but the face had a lot of dents and chisel marks with a little sway.
Not having the benefit of the internet and especially this forum, I took an angle grinder to it. I would say that I removed about 3/16 of an inch off both ends and 1/8 inch from the center. After using it for about a year when doing some heavy pounding on some 1 inch sucker rod making a large drift the face plate popped off from the sweet spot back to the hardy hole.
I was so disgusted with myself after an old time master blacksmith explained to me why that happened, was I had weakened the forge weld of the face plate when I took the grinder to it and what it would take to repair it, I gave it away.
As you say you are getting 90% rebound and if it has the same sounding ring when tapped with a hammer over the whole face you have an excellent anvil with nothing to worry about.