KB4462174 does not appear to be another Japanese calendar update fix, it's a real security fix.
Is there anyone here who is using Office 2010 on a genuine POSReady installation (not a hacked XP installation) who could make an official support request to Microsoft about this, while there's still time?!
Although Office 2010 is supposed to work with XP, IIRC unfortunately Microsoft's policy is that once an OS is unsupported, all applications running on it are also unsupported, so I don't think there's any use in an XP user complaining to them.
If it's not working on a genuine POSReady installation though, that's a different matter, for a couple more months anyway!