In a book about wedding stories, I came upon this sentence:
In the seventies, brides and grooms often stayed apart on their wedding day before the ceremony.
I have been taught that we should use distributive plural in cases like "they shook their heads," which doesn't mean they have several heads each but that, since they are more than one person, there are several heads, hence the plural. AsI was reading this book, I wondered, why not write "they often stayed apart on their wedding days" because there are more than one couple.
You can find the book online here: https://books.google.fr/books?id=S25YDQAAQBAJ&pg=PT69&dq=%22apart+on+their+wedding+day%22&hl=fr&sa=X&ved=0ahUKEwjytpu3nPPXAhXQy6QKHTr0DHgQ6AEIJzAA#v=onepage&q=%22apart%20on%20their%20wedding%20day%22&f=false