Suppose it is dependent on the source. Look up a thread by John Wann. He bought some RES for his HBG pond and ended up with BG getting in.
Edit...I was just at a fish supplier here in eastern Ohio. I was asking about adult BG 6-9" size. He said all he had was a mix bag of BG and RES. Last year when I wanted adult RES he didn't have any. Some of what I saw this year looked really good.