It won't be a post, if it were SEGA would be more transparent and it would be common knowledge.
For starters, all International versions of past Phantasy Star games had some internal development happened. In the case of Phantasy Star Online 2, it was revealed that features exclusive to past international versions like the South East Asia and Taiwan version were in fact, implemented by SEGA... publishing an online game is not as simple as giving the new region's publisher the entire source code and letting them do as they please...
Things like the Community Team and Localization have been outsourced... Community Team (GMs, Social Media, Forums, Website, Customer Support) have been outsourced to ESTsoft (check the game's credits) who will be referred to as the "PSO2 Team" in public posts. Localization has been outsourced to a team of freelancers and Lionbridge Technologies. These two companies as well as SEGA of America and SEGA Europe (who don't have quite as many roles listed on them) have been added to the North American version's credits... Microsoft wasn't.
Lastly and this is more on the technical side (and fair disclosure, this information comes from others who have taken the game client apart)... whenever a new feature was developed for international versions of the game, portions of that feature would appear on the Japanese version's source code and files as all versions of PSO2, the JP version has files referencing features found in the SEA and Taiwan version. With the release of NA, the JP version's patch now contains references to NA's new features... including the Mission Pass. The text referencing the Mission Pass even appears in Japanese on the JP client, the only thing is the feature is not made 'active' on that version as its an NA feature (NA also has dual language text support so all text referencing new features need a Japanese equivalent at least).
Hope that gets some things out of the way.