I have no idea what those channels in your area were in analog days. Here in Los Angeles, the PBS analog channel was 28; the digital was different; at transition the digital will change frequency, but it's going to be on 28.
51 is going to digital 23 and 67 is going to digital 7 too!
From what I'm seeing in Los Angeles, this would mean that 23 was an analog channel; its digital equivalent, 23.1, was on Frequency Assignment 51, but after transition the digital channel will be on 23. And that 67 is now called 7.1. Is this what's happening, or are the stations going to entirely new Frequency assignments that they've never been associated with?