If I understood correctly winglet are more efficient at cruise and for such an LR bird I'd think you don't want a "flat" wing once folding tips are deployed, right ?
Or the tip device is just missing as not needed for fatigue testing ?
The raked wingtip (while flat) adds 85% of the wingtip's length into the effective wing span. A blended wingtip (folded) adds 45% of the wingtip's length into the effective wing span.
In other words, the effective wingspan after unfolding the wing tip would be 64.8 (the length of the wing) + 0.85 * 7 (effect of span increase due to raked wingtip) = 70.75 m
While the wingtips are folded, the effective wing span would be 64.8 + 0.45 * 7 = 67.95. Those are of course rough estimates. The flat wing in this case adds 3m to the effective span over the folded (kinda blended) wingtip.
My understanding for winglets vs raked wingtips is that if you've got the space to spare then the raked wingtips are preferable. But if you've got space restrictions then winglets are better than nothing
True, the raked wingtip adds more to the wingspan for a given length and weight of a wingtip device, but it has a negative side to it, it wastes horizontal wingspan while doing so. On the other hand, a blended wingtip extends upwards, so it eventually does not waste any span. The folding wingtip of the 77X fixes this problem for the raked wingtip as it keeps it at 64.75 span limit when needed.
That's why I always wondered why the 777 (non -X model) was designed with a raked wingtip if it's limited at the 64.75m span. This 64.75m span of the 777 is actually wing+(0.8*wingtip length), so its effective wingspan is actually somewhere between 63-64m. That could've been more if they went for a blended wingtip back in the day.