Ancient history lesson:
Jast USA was one of the first eroge localization companies. It was run by Peter Payne (also owner of JList, etc. etc.).
Yes, there was an affiliation between Jast USA and JAST. Jast USA was … I don’t know the exact details, so I dunno if it was a proper subsidiary or what. But Jast USA was to Jast, as Peach Princess is to Crowd and Will. Jast USA released a lot of old games - Seasons of the Sakura, Three Sisters Story, and Runaway City - that were localizations of games made by Jast.
After awhile, Jast went under. (The founder and president died of a heart attack, I seem to recall.) So Jast USA was left without any new games. They were forced to recode an entirely new engine for Transfer Student because they had the data and the rights, but the engine couldn’t be worked on by a non-existent company anymore.
So then Peter went out and convinced Crowd and Will to work with him. He couldn’t use the name Jast USA though. So he opened a new division named Peach Princess and mostly retired Jast USA.
Recently he’s reorganized and put things mainly under Jast USA again. But yes, JAST and Jast USA were connected in the past.
Unfortunately I don’t have the Japanese names of a lot of old Jast USA titles, but if you looked them up, I’m pretty sure you’d find Seasons of the Sakura and 3 Sister’s Story (in their Japanese titles) on the list of old JAST games.