That would be because of the "conversation" field in the .utc. They may share the same name, but the contents may be very different. Like having a differently named conversation triggered. There would be no conversation the name of the Bith on Tatooine on Korriban, hence nothing would happen.
As stated, this would only happen if placed in override though, not if the file is directly added to a .mod or .rim
If for example one would place all modified NPC's of TSLRCM in override, many would override themselves (doubles of the same name) as well as even overwriting some not changed by us simply due to having the same name. Same for .dlg's, many are shared amongsts modules (Like Zherron in 601 and 602, Kumus in 502 and 503 etc. etc.) who have the exact same name, and more than a few modmakers made the mistake to drop those simply in override, breaking the entire game...
Odly enough for Telos they did name them differently (like grenn, 202grenn, 220grenn). Although there are still many duplicates, apparently from the 2 residential areas, czerka and the exchange front being orriginally one map. Same can be found on Nar Shaddaa where it really seemed like they tried to make it one giant map, rather than split up as it is now, and 301 as a result being filled with clutter from the other modules (and some of the other modules with stuff from 301 or others too), several of them outdated.
And these leftover files caused more than a few problems on those maps aswell, but hopefully we caught and elimated them all...
And it seems I went pretty off-topic there .