People in the Åland Islands are citizens of Finland, and the islands are part of the EU, but Wikipedia page on Finnish passports says that the residents of the islands have different passports than those in mainland Finland (https://en.wikipedia.org/wiki/Finnish_passport#%C3%85land_Islands). There are also a few pictures online of the cover pages of Åland passports which are different from Finnish ones. My main question is, is either the issuing country or the "nationality" on the passport marked as Finland or Åland Islands? What about the ISO3166 codes for each of these items in the MRZ?
I was unable to find a picture, but my understanding is that Åland passports are functionally identical to Finnish passports in every way except the extra "Åland" label on the cover. This includes using standard Finnish country codes inside. Per the Finnish police, which issues all Finnish passports:
Jos hakijalla on Ahvenanmaan kotiseutuoikeus, hänelle myönnetään Ahvenanmaan passi, jonka kannessa on lisäteksti Åland.
"If the applicant has right of domicile (kotiseutuoikeus) in Åland they will be granted an Åland passport, whose cover has the additional text Åland."
In general, while there are residents of Åland and the islands have a great deal of internal autonomy, they are still citizens of Finland and treated as such for all international affairs -- including passports used for travel overseas.