I have two racks that if the buck would have lived to shed, you wouldn't think they were a match set both by size diffrence and buttons. Usually the color and shape of the lower portion will match reguardless.
Some times mates are very hard to put together, other times they look like the twin side.
Based on the pictures you have above, the shape of the base or lower 6-8" is not the same... big indicator as not being a set, even if the antlers are way diffrent, they still grow off the top of the head in a similar fashion. The the color looks diffrent, less 'ivory' on one than the other, not to mention the buttons are not similar. I would say that there is a 99.99% chance that you just have singles. Get out there and find those mates!