I have not read the entire thread but the parts I skimmed conflict with policy I was recently helped with/confirmed by a CS Manager recently:
The policy I was provided indicates that in addition to the less generous policy in the thread, if:
*All passengers are *G or better OR booked in a full-fare business inventory for the UA operated flight(s), AND
* The connection time is less than 12 hours, AND
* The names on both reservations/tickets are spelled identically, AND
* The receiving airline is a UA partner OR an airline with which UA has an interline baggage agreement
UA will accept and through check luggage even on separate tickets in those cases
In my case the two specific airlines I was asking about are very definitely not UA partners but have a interline baggage agreement