The ISO rating of a film is done per ISO specs by the manufacturer. Probably not done with Rodinal.
If you follow the manufacture's instructions and use the same developer, agitation, temperature.... then you should find the speed very close to what the manufacturer found.
If you do anything else it's no longer going to match the ISO and the new number is better referred to as EI or exposure index.
Your EI is "personal" and reflects your processes, biases, metering practices, your equipment's vaugarities, the quality of water used, and more.
Finding an EI other than box speed and different than others find, that works good for you for any given combo of equipment and materials, is perfectly normal.