Rocamboles don't store as well as some types, but the issue is usually sprouting - not rotting or molding. Something else must have happened to those bulbs, perhaps the bulb wrapper was damaged by an insect, or bruised during harvest.

Two of the varieties I grow (Special Idaho and Vic's) are rocambole, and both are still in good condition. The only problems I notice with rocambole garlic is that there are often double cloves (multiple cloves within one skin) and the clove skins tend to separate easily at planting time. Those naked cloves should grow normally if planted (all of mine did).

What were the storage conditions where you had them since harvest? I store my garlic in my basement and found that if I run my dehumidifier down there 24/7 the garlic tends to desiccate by planting time in the fall. Now I run it only when absolutely required and the garlic heads including my Spanish Roja, which is a Rocabole, are still solid and in good shape come October.

Thanks for the comments. I stored the garlic heads in paper bags inside the house, same as the other 3 varieties. I dunno. Maybe I'll try again sometime.