the statement "I hope that I'm using version 2003a." indicates that we also need to include the tz version where the change was added.
How about adding a version file in the tzdata database, say _tz_version.txt, that contains something like: :::::::::: _tz_version.txt :::::::::: tzdata 2003a _tz_version.txt could be a text file that is part of the tzdata source tar file. zic could install it to the /usr/lib/zoneinfo/ (or wherever) directory. Then zdump -V (new option) could read the _tz_version.txt file, and print the version as "2003a". An inconsistency is that the files in the /usr/lib/zoneinfo/ directory are zoneinfo files, while _tz_version.txt is not. A user (or script) could try to set TZ=_tz_version.txt even though it is not a valid zoneinfo file. It could help to create a new src directory under zoneinfo, that would contain source files.