What is the correct range of the 787-10? There are two conflicting values for the 787-10's range; they are:

6,345 NM (11,750 km) -- boeing.com

7,000 NM (12,975 km) -- on the same website few years ago, as well as flightglobal.com


Note: In its early development the value was 6,345 NM (11,750 km), same as #1.
Which is correct and why do the values keep changing?
The range of an aircraft depends on the payload. The value you typically find is the range at typical payload.
You can find the payload/range diagram in the Boeing 787 Airplane Characteristics for Airport Planning document:

As you can see, at maximum zero fuel weight, the 787-10 range is only ~4200 NM. According to Wikipedia, the typical passenger configuration for the 787-10 is 330 seats in a 2-class layout. Assuming 195 lbs per passenger (FAA average adult passenger weight in winter) plus 50 lbs baggage per passenger, gives a typical payload of 80,850 lbs. This would result in a range of ~6000 NM. If not everyone onboard is an adult and not everyone takes the full 50 lbs for baggage, the range can be higher of course. Completely empty, the 787-10 can easily fly over 8500 NM.