Preheat the oven to 350 degrees F (175 degrees C).

Heat dates, 2/3 cup brown sugar, orange juice, and orange zest in a saucepan over low heat; cook, stirring occasionally, until dates have softened, absorbed the liquid, and mixture is like a paste, about 10 minutes. Remove from heat; stir in vanilla.

Stir oats, flour, 1 cup brown sugar, baking soda, and salt together in a bowl; cut in butter with a knife or pastry blender until mixture resembles coarse crumbs.

Lightly press 2/3 of the crumb mixture into the bottom of a 9x9-inch pan. Spread date mixture evenly over the crumb crust; sprinkle remaining crumbs evenly over the top of date mixture.

Bake in the preheated oven until top is golden, about 30 minutes; cool on a wire rack for at least 1 hour before slicing into bars.