Yes, that's correct; in official documentation and reference, the "USS" prefix is very specifically applied only to commissioned warships. New ships, prior to being commissioned, use the prefix "PCU" for "Pre-Commissioning Unit," and following decommissioning, gain the "Ex-" prefix. So, the CONSTELLATION went from "PCU CONSTELLATION" during construction and trials, to "USS CONSTELLATION" while she was in commissioned service, to "Ex-CONSTELLATION" once she was decommissioned. Now, in informal discussion, it is fine to say "USS Constellation," like in a news story and the like (note the lower-case spelling...intentional...ship names are always in ALL CAPS when discussed in naval correspondence), but I have a habit of falling into the formal style since it is what I deal with on a daily basis
.
I think it was the ENTERPRISE we were discussing when you visited Norfolk; at the time she had just entered Newport News for inactivation.