Thanks for the info, everyone.
I want to stress that I'm NOT accusing Dunn's of shorting me. I didn't weigh them and I'm not confident in my ability to eyeball them. I don't want to accuse them when there's a chance they did nothing wrong.
I've floated some pallets along with my shallow brush piles to encourage spawning. Hopefully these minnows will establish well. If not I'll put some more in when I stock my bluegill.