Also, you have to be sure that what you are stocking are the actual bluegill that you want, and not some variant or cross.
Yep.
If you get a large load of BG from a fish supplier there is a chance a few GSF or other undesirable fish could be hidden in there.
However, you are essentially hand-sorting every BG you stock by your fishing method. Just be sure you are correctly identifying pure strain BG before you drop them into your "keeper" bucket.
Also, if your description of the source pond is correct, then I agree with Sunil that those BG are probably stunted. However, that may actually be a good thing. Those BG will reproduce in your pond, but they will be growing slow enough that they will be "eating size" for your growing bass at an earlier date due to their stunting.
