I'm looking at
https://packages.debian.org/buster/isc-dhcp-client and I see that there was a binary NMU - 4.5.3-3+b1 - but when I click on the "Debian Changelog" link on the right-hand side under "Debian Resources", it takes me to the changelog for 4.5.3-3, not 4.5.3-3+b1, which is what I was expecting.
I'm not sure if this is expected behavior or not, but the people who can fix it if it isn't aren't going to unless somebody tells them about it, so here ya go.