The short answer would be that the measured amount of lead that went in when it was built was probably accurate.
The brochure would state, as accurately as reasonable, the total dry weight of everything else that gave a displacement weight for a finished boat. This would not reflect the in-use total displacement which adds water, fuel, personal effects, instruments, and maybe options like the spinnaker package stuff or larger winch upgrades.
Add a little water absorption in the bottom paint over the decades and all the beer and spare lines, anchors, chain and whatnot... and you quickly get to another thou or so.
Back at the factory (any factory), it is also common for a finished boat to slightly exceed the design weight. Enough so that Ericson bragged in a full page ad for their E-33RH that they had produced that model at the designer's calculated total displacement.
Those emergency cans of Dinty Moore beef stew really add up, don't they?
Note B: those well used load cells on the average Travelift may or not be close within a hundred # or so. At best.
Note C: during one of the lifts for our boat ("10,600 # displacement") I asked the operator about the indicated weight, and he said that based on a couple decades of experience with that rig, and after interpreting the dials, he would state that ours weighed in at about 11K or so.
