I've now found that if I go to the apparent CC default settings (CC1, digital and primary) and view the STB output using the EH55 composite audio and S-video connection outputs to the display the CC appear. Of course the video is standard def and of S-video quality but it is certainly watchable. Neither Comcast nor Panasonic tech supports have been able to assist me in trying to optimize the CC.
Could it be that, like HDMI, component connections cannot deliver CC to my display? I've read about the HDMI issue but was unaware that component connections might present a similar difficulty.