I've attached two screenshots showing me playing a co-op map/chapter alone. I disabled the bots for this test. What I did here was spawn just 1 Tank, 1 Hunter and 1 smoker. That gave me a total number of 3 kills on the stat screen for "general defence" and "special killer" - these are the values that should be zeros for both stat screens (sry, I forgot to add the Boomer to this kill count, but the same would apply to him as well).
As for the HP damage on the Tank I don't know if it resets to zero or not. Usually for me the load times between maps are quite short on my server. What I'll do is try and find a very large add-on map to increase the load time, and report back here with the Tank HP results and another screenshot for Tanky as well.
https://www.dropbox.com/s/pbce4721cx...illed.jpg?dl=0
https://www.dropbox.com/s/7ovkyroj4j...0only.jpg?dl=0