Pines have a hard time pulling on the water chain due to their needle design (silhouette/waxy coating). To move water to a location on a pine branch, you usually need needles or a strong tip bud that was already emerging just as the needles were lost (i.e. the needles already drew a lot of sap to that location just before their demise). If at a given junction you can trace to a descendant shoot that is green / has needles, then the live vein traces through that junction. If no descendant shoot with needles, you're looking at dead wood and inspecting under the bark won't find any trace of green cambium, or only fading cambium.