If no date is found on a print item, write n.d. instead of a date. If no date is found on an online item, include the accessed date (if not already included in the citation).
If no publisher is found, write n.p. instead of a name.
If no author is found, omit that portion of the citation. If the item's author is listed as "Anonymous" on the title page, then you may write Anonymous instead of an author.
Do not make up information for a citation. If the item is missing information, do some research and see what you can find out from other sources, such as a library catalog. If you still cannot find the information, you may omit that part of the citation (excepting publisher and date, as noted above). If you're unsure or wonder if you're missing something, this would be a great opportunity to meet with an Oberlin librarian.
From CMOS 13.23 [emphasis mine, note the changed guidelines for the 18th edition]:
In a note that cites a book with more than two authors or editors (in previous editions it was more than three), list only the first author or editor, followed by “et al.” (Latin for “and others”). In the bibliography, list up to six authors; if there are more than six, list only the first three, followed by “et al.”
If you're needing help citing an item that's not included in this LibGuide, you probably aren't alone! Please email Con Librarian Krista Mitchell if you notice an item type that you think should be included or make an appointment with a librarian for further help.