Terry Watson was a flight controller during Apollo. In an Apollo forum, in response to a query regarding the ability of the CSM to be controlled from the ground, he gave some additional info below. I thought it was well worth sharing.
"Our ability to control the CSM/LM didn't change much at all over the Apollo missions. Changing anything in the hardware or software was a very expensive proposition. You couldn't just upload a new flight software version as simply as we can today. Same with the hardware. Things didn't change much with the flight hardware unless there was a serious reason to do so.
As far as monitoring the CSM/LM, things did change on the ground over the program, and I will share a little tidbit that might not be widely known. If you listen to some of the audio tracks of early Apollo, sometimes you will hear the Flight Director asking flight controllers to release any unnecessary displays. This was because the MCC could only generate a total of 28 different display pages at any time. Of course, one display could be monitored at a number of consoles. Each MOCR position was assigned a maximum number of displays that we could request at critical mission phases. I recall the GNC area got 2 displays. The FD request to release some displays would come when one area needed to bring up its maximum number of displays, and some positions or back rooms had brought up additional displays. Now for the reason we were limited to 28 displays…
The CRT display system was a combination of "digital" information, mechanical devices, and video feed. There were 28 machines in the bowels of the MCC that were used to generate each display page. The machines looked pretty much like a locker you might have had in high school. You opened the door, and at the bottom was a CRT facing upward. At the top of the locker was a video camera looking down at the CRT. Just above the CRT was a transparency machine. When a flight controller dialed up a display, the request would be routed to an available machine. The transparency machine would slap a pre-printed slide on top of the CRT, which contained all the data "labels" , display name and MSK number, any graphics, etc. The RTCC would then generate the digital data on the CRT. The video camera at the top of the locker would then transmit the combined information to the MCC consoles that wanted to look at it.
The RTCC, as big as it was, was not able to generate the dynamic telemetry data and all the background text. It wasn't until sometime in the Apollo program, where the display system went all digital. The earlier system was not as clear and crisp, as it went through 2 processes. Additionally, the machines would hang up sometimes and display the wrong background info, and we would notify an RTCC guy to reset it.
The easiest way to tell the early displays is that there were alignment "targets" on the corners of the background slides, and both the slides and the digital data displayed the MSK number. You will see 2 MSK numbers on hardcopies from the earlier system. The all-digital displays were significantly better!"
