Here’s the trendline: A significant shift in Pre-Black Friday sales has occurred over the past several years as retailers move from a cascade of big one-day promotions to deals that “drip” over a longer time period. Pre-Black Friday in the Rear View Mirror When you look back to 2017, the Black Friday event looks primitive by today’s standards. Retailers provided ad previews a few days before Black Friday and encouraged consumers to come into the store the evening of Thanksgiving Day to get first dibs on discounts. It seems quaint now but …