You can use the command M-x change-log-merge to merge other log files into a buffer in Change Log Mode, preserving the date ordering of entries.
Versions of Emacs before 20.1 used a different format for the time of the change log entry:
Fri May 25 11:23:23 1993 Richard Stallman <rms@gnu.org>
The M-x change-log-redate command converts all the old-style date entries in the change log file visited in the current buffer to the new format, to make the file uniform in style. This is handy when entries are contributed by many different people, some of whom use old versions of Emacs.
Version control systems are another way to keep track of changes in your program and keep a change log. See Log Buffer.
