The example document in the HTML+ spec (1993) did not use them: https://www.w3.org/MarkUp/HTMLPlus/htmlplus_7.html
The HTML 2.0 spec gives this as its first example:
<!DOCTYPE html PUBLIC "-//IETF//DTD HTML 2.0//EN">
<title>Parsing Example</title>
<p>Some text. <em>*wow*</em></p>Certainly by the point of HTML 2.0 (November 1995; the first non-draft spec for HTML) all three elements have start and end tags all optional.
The more general ability to omit start/end tags from given elements is a feature of SGML (October 1986), and HTML 2.0 to HTML 4.01 were defined as SGML applications (though approximately nothing ever used an SGML parser for HTML).
You're commented needed to modified for current times. ;-)
If this was truly the case, we wouldn't need things like Applitools to view our HTML documents in various browsers to scan for differences.
Note though that there are some conditions.