They started with a sequential numbering system. The first two digits are the model (C11) and the next four are the sequence number. The school where I teach has S/N 4, which was donated by a family with kids in the school. Their uncle knew someone at Celestron, and got one of the press loaners after they were done with them. It has phenomenal optics.
They came out around the time that I was working in the scope shop, and it was known then that they were somewhat variable in quality, so we didn't carry them.
The donation of this one began with the dad asking me if I the school could use a large telescope. Knowing that people often describe a 60mm f15 refractor as large, I asked, "How big around is it?" He held up his hands to about 15" in diameter. So the next question was, "What color is it?" to which he replied "Orange." So I said, yes, we could probably use it (with visions of students looking through a C14). A while later I walked into the lobby and found the filthiest, most neglected C11 I had ever seen. Since I knew the orange ones were iffy, I thought, "What have I gotten myself into with this?" But then I turned it around and saw the serial number, and my jaw dropped. After many hours of cleaning, re-greasing, etc., it went into service.
It is incredibly heavy, and quite a challenge to lift onto the wedge. The family actually donated an Exploradome (when they first came out, they had a very deep discount for schools) to house it, since it was too much to regularly use otherwise. Like the Orange C14, it actually works better to loosen the forks, remove the OTA, put the mount onto the wedge, and then re-mount the OTA.
A few years later I had a similar experience - someone had found a large blue telescope on Freecycle and offered it to the school. I told them to bring it in and I'd look at it. Again, an absolutely filthy, run-down, scope. This one, an 8", in a crude ATM sonotube and plywood mount. "Oh no, what have I gotten myself into?" Then turn it around and there's this: