Heat oven to 400 degrees. In a medium saucepan over high heat, combine vinegar, brown sugar, rosemary, and pepper. Bring to a boil; then reduce to a simmer until sauce thickens to a syrup, about 15-20 minutes. Remove from heat and let cool to room temperature.
Parcook bacon; then remove to a plate lined with a paper towel. Slice bacon in half diagonally. Place one chorizo piece inside the “pocket” of each date. Wrap with bacon and secure with a toothpick.
Bake dates until bacon is browned and sizzling, about 5 minutes. Drain on a paper towel; then drizzle with balsamic reduction sauce.