Cash Shop Specials 7/15 - 7/21

so bonus potential cubes weren't a permanent addition to rewards shop?

Nope. They never showed up, and when people asked about it on the official forums, Artasi said something like, "Sorry, that was a mistake, they were intended for a Daily Deal later this month." (Which pretty much confirmed Miracle Time)

Probably better this way. If people had used up their Reward Point Bonus Cube allowance before Miracle Time, they'd have gotten quite upset.