Traveled SIN-HKG-XMN in Y today with the first leg on United and the second on Xiamen Airlines (MF, Skyteam).

Asked at SIN if a bag could be checked all the way through to XMN even though I had separate tickets and no HKG-XMN boarding pass.

The United agent just looked at the paper copy of my HKG-XMN e-reservation, pulled the flight number and said no problem.

She did tell me to check at the HKG transfer desk to see if I had to reclaim the bag or not.

In HKG, the transfer desk just copied the baggage tag number and said that the bag would be automatically transferred.

Showed up in XMN as promised!