Sounds like your pond was a "clean slate" to start. Any chance GSF have come in from upstream in the water supply to your pond? Any chance fish have come in from downstream? Some fish (like GSF) are sneaky bastards and will swim upstream during flood stage at your pond outlet and can make it into the pond through surprisingly shallow flows of water.
If your pond still has zero outside fish introduced since the last draining, then either a few Hybrid BG or a few GSF did get in during your stocking.
IF those fish are the cause of your BG not doing well, then that problem should be self-correcting. Your BG will massively outbreed both the HBG and the GSF.
However, the most common cause of BG not doing well ... is too many BG.
Maybe read up on some threads about Relative Weight. It is the easiest way for average pond owners like me to evaluate our fish populations.
If you are catching underweight BG, then something is hurting the health of your population. If you are catching fat BG, but they are all small/young, then perhaps your bass population raced ahead of your BG population. When that happens, the bass may have eaten most of your large (original) BG. However, the BG still usually breed enough to catch up with the feeding requirements of your bass. You also need to track the sizes and relative weights of your bass. That gives you info on your bass AND info about your BG.
Finally, maybe try fishing specifically for some of your shellcrackers. Sure would be nice to see how they are doing.
