When you need to list more than one item in an element, separate the items with commas. Thus, if you need to provide two original publication dates in the middle optional-element slot, as you might if you are citing two works combined in one volume, list them as shown in the following example:
Coolidge, Susan. What Katy Did at School and What Katy Did Next. 1873, 1886. Wordsworth Editions, 2001.
Published 7 September 2020