These are the files connecting the mainland (and mainland plus preview) to Vvardenfell and internally. This changes dialogue. Do not edit this file without also loading TR_Mainland.esp, and do not merge other esps into it, period!
An ods is part of the download. This file takes precendence over maps you find on this site or on UESP, it even takes precedence over the content of the esps. If they diverge, the ods is correct.
The files need only be updated when more landmass moves into TR_Mainland (both) or new settlements make it into TR_Preview (P&M).