They're correct, what you read is wrong. What you may have read, and was the subject of a recent thread on this forum was about the 5 wire system. Some of the older wiring, CHANGED OVER TO AC IN THE 30's, existed in the older sections of Washington, DC (and I'm sure other old towns) for a long time. I was involved in the early 70's with conversions of these old systems, but I don't think many were around long after that.