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Here are the original descriptions of the old LaTeX version.
 \begin{macrodesc}{versionadded}{\op{explanation}\p{version}}
 The version of Python which added the described feature to the
 library or C API. \var{explanation} should be a \emph{brief}
 explanation of the change consisting of a capitalized sentence
 fragment; a period will be appended by the formatting process.
 When this applies to an entire module, it should be placed at
 the top of the module section before any prose.
 \end{macrodesc}
 \begin{macrodesc}{versionchanged}{\op{explanation}\p{version}}
 The version of Python in which the named feature was changed in
 some way (new parameters, changed side effects, etc.).
 \var{explanation} should be a \emph{brief} explanation of the
 change consisting of a capitalized sentence fragment; a
 period will be appended by the formatting process. This should
 not generally be applied to modules.
 \end{macrodesc}
Adding a parameter is explicitly a "versionchanged" kind of change.
Since the Sphinx items are supposed to be equivalent, this has always been the intention, even if the current devguide deviates.