As Ray said, it's all about food and fuel - how ready the plant is at the point that something triggers spike development. But even in a batch that has been grown together since deflasking that doesn't necessary mean the genetically gifted ones necessary get more spikes. Even in a bench of clones some will out-perform others. Perhaps some were bigger coming out of flask, some got a little less sun or water or fertilizer because of position, a few had to fight off a pathogen. Some may be genetically predisposed to get 2 weak spikes instead of 1 strong one given the same resources, while others tend to get a single (potentially huge) spike no matter how strong. Of course, when you're picking 1 plant off the bench to buy you go for the big healthy one with 2 good spikes, but even then it may be a great performer in ideal greenhouse conditions but not the best choice for your windowsill. When you observe a plant through several seasons and it always performs better for you then the genetics do match your conditions better than others, but that first bloom seedling isn't necessarily a predictor of that.