Which innovative pricing strategy did Bloomsbury Publishing use for the Harry Potter series that helped transform it into a global phenomenon?

The publishing industry employs fascinating pricing strategies to maximize sales, build reader loyalty, and create cultural phenomena. J.K. Rowling's Harry Potter series demonstrates several innovative approaches that transformed not just the author's fortune but revolutionized book retail marketing. This question examines a unique pricing strategy employed for the series that helped cement its place in literary history and retail innovation.

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They released adult editions with sophisticated covers at premium prices while maintaining standard children's editions, effectively creating two distinct market segments
They priced each successive book 20% higher than the previous one, creating a sense of increasing value as the series progressed
They initially sold the first book at a loss to build readership, then gradually increased prices for subsequent books once brand loyalty was established
They implemented surge pricing during release events, charging premium prices for copies purchased at midnight launch parties