Each box was $23 so $46 - $10 = $36 + tax.
$36.00 / 256 diapers ~ 14 cents each.
Other sizes also qualified for the promotion, but their individual prices were significantly higher. For example, a 148 pack of size 1 was $40. Luckily, Target PM'd Amazon's price of $32/box, making 2 boxes of size 1s come out to $64 - $10 GC = $54 / 296 ~ 18 cents each.
Hopefully you guys can replicate the deal. Link to Target's website for reference, but this was B&M