They possibly need to be cured in Spain so that they can be called Spanish (e.g. Serrano or Ibérico).

And I guess they aren’t fungible because they get tested for health reasons and protein content.

In the EU, tracking is needed. If people get ill from eating ham, it’s important to exactly know where the meat came from (factory, farm, sometimes even the specific pig. Conversely, if animals get ill, it’s important to know where their milk went. https://ec.europa.eu/food/animals/traces_en)