Measure of a ManEdit

Is there any reason why the USS Excalibur NCC-21534, active in 2365 (Measure of a Man), is automatically assumed to be the same as the Ambassador-class USS Excalibur NCC-26517 (Redemption Pt.II), undergoing repairs in 2368? Why not have them as two ships, as their registries indicate? Catiline63 (talk) 22:05, January 5, 2013 (UTC)