Which early 20th century retail innovation is widely considered the first significant step toward modern customer personalization techniques?

Throughout history, retail has evolved dramatically with innovations that transformed how merchants connect with customers. Long before digital algorithms, certain historical developments laid the groundwork for today's personalized shopping experiences. This question focuses on a pivotal retail innovation that fundamentally changed how businesses understood and targeted customer preferences in the early 20th century.

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The creation of direct mail catalog segmentation by Montgomery Ward in 1908
The introduction of Sears' customer loyalty cards in 1916
Woolworth's implementation of customer purchase tracking in 1922
A&P's regional product assortment strategy launched in 1927