For a new or empty pond, the usual order is: stock minnows and let them get established, then stock BG and let them get a start, then stock your top predator (usually LMB).

If the pond already had a large GSF population when they tried stocking BG, then there is a chance that the GSF managed to eliminate the BG before they were able to establish a sustaining population.

The GSF may also be keeping your crappie population in check. Without minnows or small BG to provide forage for the GSF, you may have thousands of stunted GSF in the pond. The cannot eat the large crappie, but they can wipe out the crappie fry and crappie fingerlings very efficiently. A few crappie do get through and that is your supply of rare, large crappie. (Speculation on my part.)

My advice would be to keep fishing for BG to determine their presence and size/condition. I have fished with little kids in small ponds where you had to catch about 10 GSF off of a single cedar tree before the kids could catch any BG! Frequently, you could even tell by the bobber movement if it was a GSF or BG sampling the bit of worm. (When my #2 daughter was little, she used to call the BG, "sneaky fish", because they were more difficult to hook than the more aggressive GSF.)

Also try to determine if the GSF you catch while fishing for BG are all about the same size and a little skinny. (That will suggest the GSF are stunted.)

If you do NOT have a good population of BG, then one option would be to stock some larger, feed-trained BG and add a feeder to your pond. On a quality feed, your BG will grow very rapidly. They should then be able to establish a reproducing population. If so, it may take several years, but they should be able to out-breed your GSF and become the dominant panfish in the pond.

If you do get some comprehensive sampling of your fish populations, and are considering the plan I described above, then you should probably start a new thread on that specific topic. There are lots of experts in the forum (not me) that could help you evaluate your proper stocking sizes and numbers of BG to give you a good chance of getting them established in your pond.

P.S. As your pond shifts more to BG and away from GSF, that may also help your crappie population. (Hopefully!)