I think the manual should include additional information, probably in the installation section. It would be useful for readers to point out that cataloging framework and indexes are based on the UNIMARC defined by IFLA and do not take into account the modifications commonly implemented in different countries using the format (France, Italy, Portugal...), and that adaptations may need to be made by libraries or support companies. Unlike Marc21, there are multiple variants of UNIMARC, and no one uses IFLA UNIMARC as is, so the default config of Koha is not suitable out of the box. For example in France and Italy the use of field 359 is not the same. There is an even greater need for adaptation in countries that do not use UNIMARC directly, but rather national formats based on UNIMARC with variations (Russia, Slovenia, Korea, etc.).
The information in the manual could be brief (such as a warning note), possibly with a link to the wiki for very specific details on implementation in different countries.