The seized valve phenomenon is something I have seen on all Power Stoke engines - four 7.3L engines, two 6.0L engines and one 6.4L engine. Out of those I only had one where I could not get the valve to move and come out which was on a 7.3L. The rest were removed and replaced with new valves and I honed the valve guides with a transmission valve body hone I bought just for this purpose. It works fantastic and I have never had any of those engines return.
Incidentally only two of those engines were brand spanking new, one a 7.3L came off the car carrier popping out of the intake and the last was a 6.4L that was on our lot a month or so. As a matter of fact that truck was sold to an overhead door company and was parked outside my shop a week or two ago as they repaired one of our shop doors.