Preserve the original bytes first

If item or mob names change into replacement characters or unreadable symbols after an import/export, stop and keep the original file. Saving already damaged text as UTF-8 cannot recover bytes that were lost earlier.

A practical check
1. Make a copy of the original file.
2. Open the copy using the encoding expected by your own client/server workflow.
3. Compare a few known names, tabs and line endings.
4. Export a small sample and reopen it using the intended target encoding.
5. Check the text diff before replacing a production file.

The M2City checker offers UTF-8, Korean/CP949, Windows-1252, Windows-1250 and UTF-16 LE decoding. This is a selection of supported decoders, not automatic proof of your file's encoding. A warning about replacement characters means you should try the correct decoder or inspect the original export.

Keep numerical and text problems separate
A VNUM can remain readable while its associated name is damaged. Conversely, readable names do not prove that an upgrade target exists. Check both independently.

If you need help, post a tiny sanitised example and explain where the original file came from and which transformations you applied. Never overwrite your only copy while experimenting.