The plane is signed to Kalitta until they release it back to Baltia, which is why the flight to Ypsilanti was under a Kalitta call sign. Kalitta can test fly planes under their ferry permit even before the maintenance is completed, so it's not a guarantee that Kalitta has signed everything off yet. It's also very possible that Kalitta accomplished their maintenance checks on the way to YIP and signed it off when they got there. We won't know until Baltia announces that it's done.