Remember 1975? Me neither, even though I did live through it. But I'll tell you one American institution that surely remembers that particular year, the U.S. concert industry. And here's why: If you average out the year of peak popularity for seven of the biggest acts playing on various Triangle stages over the coming week, it comes to...1975. That's right, 37 long years ago. For more particulars, see this story in Friday's paper.