Wow! Thanks!
Added your code and edited mine to fit it, and I get numbers that are closer to what I'm expecting. I'd love to say they're perfect, but now it appears that each value is in my list with its count value doubled. (Of course, I have the occasional 3 or 5, but I think I know where those are coming from.)
What's happening is that some packets are nearly identical to each other, so when packet X is tested, the map finds N matches with packet Y. But, when packet Y is tested, the same N matches are found with packet X. I'll bang my head on the desk for a minute or two and see if the answer rattles loose.
Again, thanks for the help. Not only did it correct the behavior, but it's ever so much more elegant. Too bad I've already used my votes today.