I'm pretty sure N221UA exited with Domestic configuration when through heavy maint - seat map was not updated on departure, but that isn't unusual after a mod.
Why would UA not convert the unit and send it through HKG heavy maint, which are all done in HKG and XMN? N222UA did get domestic config at HKG in 2020.
N219UA and N220UA are now in HKG - if mod being done, all four would be ready and complete all 772 conversions