Grafted trees, or seedlings?
If seedlings… they are their own ‘variety’…kind of like… your children are not you.
If grafted… you might be able to identify some varieties by nut characteristics.
Productive pecans are heavy nitrogen feeders. Soil testing and appropriate fertilization may help ‘push’ growth on your 12 ft tree, but it’s also possible that it’s on an inferior rootstock, or planted in a less-than-ideal spot.