Reno, I just recived a mail from a friend of mine and this is what he wrote:
"I pulled out my copy of William Hess' 'P47 Thunderbolt At War' to check out what Blakeslee said about the first P47 victory. Don't know whether you've seen it but Blakeslee describes the action of 15th April 1943. After shooting at the '190 he says it "lurched sharply and a fraction of a second later crashed into the ground exploding." I don't see how he could have mistaken that- but your text seems to imply he didn't get a victory because all aircraft of II/JG1 returned to base safely. Perhaps he shot down an aircraft from some other unit- who knows?"
So, who knows?
No further details on Heessen's involvement, though.