Your experience is one reason why I will never order drum sticks (or cymbals for that matter) online.I ordered a pair of Vater Fusion sticks a while back. When I unsheathed them, I noticed a weight discrepancy immediately. I placed them on a postal scale, and, to my unspeakable horror, one was 46 grams, the other 52. That calamitous day marked the conclusion of my experimentation with Vater.
I know you are extremely happy with Ahead sticks, and I'm certainly not suggesting you try again, but it is possible that Vater may not be responsible for the varied weight difference (under the following condition). If you ordered the sticks from a company that also houses retail space then what might have transpired was at various times in-store customers were unsheathing multiple pairs of the sticks, laid them out, and played with them.
When they were finished, they just started to put them back in the sleeves without any thought given to matching pairs. Voila...mismatched pairs. I've seen this scenario too many times at Guitar Center. The employee who picked your order just grabbed a pair of sticks and sent them out to you.
Of course...if the company you ordered the sticks from doesn't have retail space, then the point is moot...so go ahead (no pun intended), and blame Vater. They would deserve it.