re: Numbers vs. names -- You may remember...
The Apollo missions were numbered. The crews, however, were free to dub their orbiter and lander with call signs (Gumdrop and Spider, Snoopy and Charlie Brown, etc.) for communication IDs.
Apollos were one-flight-only spacecraft and completely interchangable, as (I presume) the Orions will be. The only time NASA has had spacecraft capable of multiple flights -- the Shuttles -- they were given permanent names.
Even so, the STS missions are still numbered, and retain those numbers even when they fly out of sequence.