Original date of a previously unpublished work
How can Zotero be used to include the date a work was written, even if it was not published until much later? For example, I have a paper originally written in 1960 that was only published posthumously in 1977. If I use "original-date" in the extra field, it generates a reference that days "(Original work published 1960)," which is not correct. I'd like it to read "(Previously unpublished manuscript written in 1960)" or something similar. I use APA and Chicago styles.
References: Previously unpublished manuscript written in 1960
that will work in APA style