Terran-Vasudan ships always need names, considering Terrans always have the "naming cerimony", I assume Vasudans would too, or else Terrans would give them names. Shivans however, are given the name of Terran designations, it helps you remember them, specially if they appear in more then one mission. However, it really helps the mission and the campaign if you give everything a name. Its not that hard really.
General rule of thumb is a craft should never have a number in it unless its part of a wing. Additionally, names should never be duplicated (exception of wing names), and the crafts type should never be its name... unless its a first encouter of an enemy vessel, or its a one of a kind allied vessel (Colossus, etc)