My very first M&B award trip on a *A partner was during Easter 2019 and there were both a slight schedule change (departure pushed forward by some 10-20min) as well as equipment change and with that also a seating configuration change and therefore needed to select seats again (got the emails well in advance). However since the tickets were issued via M&B (operating airline was LOT btw) they did have a 390-number, as did basically all of my other redemptions on *A partners with Miles&Bonus after that, including one with UA! And when I say *A partners I mean that the entire itinerary has always had exclusively *A partners and no segment operated by Aegean at all. So I don't know if anything has changed, but this would be news to me if M&B redemptions issued non-390 ticket numbers.