If an incoming letter mentions an enclosure but it is not present in the folder, make a note in the abstract: Enclosure not with letter.
Mention any handwritten notes or corrections on documents in the abstract, except for filing instructions at the tops of documents (General, Personal, name of client).
Include spaces after the period for initials in names (e.g. W. E. B. Du Bois - correct, W.E.B. Du Bois - wrong).
If you come across a stack of form letters (same content) addressed to many people, catalog those as one record with title “Letter from XXX to multiple recipients”. Based on interest of content and amount of names, make a decision on whether to include recipients' names in the abstract. Add genre term “form letters”.
Names or words with diacritics need to be encoded. Use the Oxygen character map (under the Edit menu) to look up the code that properly inserts the accented character. Use the “decimal” (not hexidecimal) code. To make sure it is searchable in Credo, use the plain text version in the abstract. Example: Pelé in title and name elements and Pele in abstract.
For royal/titled names that are in LOC Name Authority, it's a good idea to check the MARC format to see how LOC has parsed the name elements. Example: “Wellington, Charles Wellsely, Duke of, 1945-” (LOC). Title: “Letter from XXX to Charles Wellsely, Duke of Wellington”