The default sort order on Tools > Letters and Slips (i.e. tools/letter.pl) sorts by branch first, with 'All libraries' sorting above all other branches. This has the effect of hiding branch specific letters, because they sort to the bottom of the page... however when letters are processed, branch specific notices are chosen *before* the generic 'All libraries' notices. I would like to see 'Code' be the default sort field, followed by branch, so that all notices with the same code sort together, by default.
I think this is no longer valid. The Notices and slips table now is sorted by Name by default, and this can be easily configured in the Administration -> Table settings page /cgi-bin/koha/admin/columns_settings.pl?module=tools&page=notices&table=lettert