Different
versions of import utility are upward compatible. This means that one can take
an export file created from an old export version and import it using a later
version of the import utility.
This is quite an effective way of upgrading a
database from one release of Oracle to the next.
Oracle also ships some previous catexpX.sql scripts that can be executed as
user SYS enabling older imp/exp versions to work (for backwards compatibility)
For example, one can run $ORACLE_HOME/rdbms/admin/catexp7.sql on an Oracle 8 database to allow Oracle 7.3 exp/imp utilities to run against an Oracle 8 database