Products with best before dates can still be consumed past their date, as there are no safety issues associated with the product. If the safety of the product was to be compromised, a use-by date would be used instead.
Product past its best before date may experience some quality deterioration over time. If the product has been kept as recommended and not exposed to elevated temperatures and humidity, quality deterioration is minimal. The product hence would be fine to consume. With Baking Powder, baking reactions may not be as pronounced as compared with product still within its shelf life.