clarify whatsnew

Author: JustinZhengBC

doc/source/whatsnew/v0.25.0.rst

@@ -397,7 +397,7 @@ Reshaping
 ^^^^^^^^^
 
 - Bug in :func:`pandas.merge` adds a string of ``None`` if ``None`` is assigned in suffixes instead of remain the column name as-is (:issue:`24782`).
-- Bug in :func:`merge` when merging by index name would sometimes result in an incorrectly numbered index (:issue:`24212`)
+- Bug in :func:`merge` when merging by index name would sometimes result in an incorrectly numbered index (missing index values are now assigned NA) (:issue:`24212`)
 - :func:`to_records` now accepts dtypes to its `column_dtypes` parameter (:issue:`24895`)
 - Bug in :func:`concat` where order of ``OrderedDict`` (and ``dict`` in Python 3.6+) is not respected, when passed in as  ``objs`` argument (:issue:`21510`)
 - Bug in :func:`pivot_table` where columns with ``NaN`` values are dropped even if ``dropna`` argument is ``False``, when the ``aggfunc`` argument contains a ``list`` (:issue:`22159`)