Not to answer for bosk, but, well, as far as I know, albums on Japanese market cost a lot more than your usual run-of-the-mill ~$15, so in order to make it worthwhile for Japanese listeners, the label would often push the band to add some bonus material for Japanese versions of the album. Usually it results in a bonus track or two added, which are not released elsewhere. A lot of bands do that nowadays, so that would be a reasonable assumption.
Looking forward to the interview!