Hi Malanowski,
There are compare tools, if you are using GX IEC Developer you can select Project > Other > Verify which allows you to compare two offline projects, this will also present you with the differences.
If you use GX Works2 or GX Works3 you can compare two offline projects by opening one project and then selecting Project > Verify to compare with another.
If you need further assistance please feel free to get in touch!
http://www.jvcontrols.co.uk