Copyright dates indicate the publication year, not the time of its writing, which might be two to three years before the copyright date. Although a recent copyright date is no guarantee of a book’s relevance or sensitivity, copyright dates are useful information. More children’s books began to reflect the reality of a pluralistic society and nonsexist and non-ableist perspectives in the 1970s.
To hear that we are only 50 or so years removed from the beginning of when authors and society as a whole decided to be intentionally inclusive about literature is truly horrifying. This reminds me that as sophisticated as we think we are as a society, we still have a ways to go. Books truly are a sign of the mores and beliefs of a nation. By looking at a book, you can sometimes get a good idea as to how a society functioned. You get an idea if whose stories were upheld and whose were omitted. Books that would be considered politically incorrect now, were just a normal sign of the times back then. Looking at a book's copyright date is a great way to gain insight into the historical context of a society.