I have a vintage set box with the kids on it. Should I continue collecting era appropriate pieces to refill it?
Given the quality of LEGO bricks, I would argue that an original box filled with the correct amount of the correct bricks from the same time period as the box is INDISTINGUISHABLE from an opened box containing the original bricks after use, and as such I would recommend you continue your effort. Just make sure that the bricks are indeed from the correct period (i.e. Colors are right, LEGO vs. Pat. Pend. Vs no markings, hollow underside or tube or lattice, etc.). The only way for a collector to be absolutely sure of the authenticity of the box and its content is to buy a factory sealed box, which are extremely rare given the age.