Thank you for all the details.
It seems that you have a good understanding for the change and why it happened, so I won't go into that.
When we do updates like this we usually post the changes on the Challenge checker forums which are followed by the volunteers creating challenge checkers. It's then a collaborated work to make sure that everything that the change affected, in one way or another. Sometimes it's as easy as rename something in the challenge checker, but sometimes it changes the challenge itself and we'll have to consider if the challenge should be archived, updated, or we if we can create some legacy solution.
Imagine for example two counties in a state merging, where the challenge was to log them all. Do the want to decrease the number of required counties then? It's not obvious. Even less obvious if the challenge was to log a certain amount in different counties.
Together with the post about the updates we usually post a list of known affected challenges. We did so with this update as well. However, the three you found wasn't detected, and I don't know why. Today I did a search for Hartford County in the checker tags and found 28 active ones. All these are likely to be faulty. This far I have looked at 6 of them, all being challenges to log capital counties. Those should be easy to fix and we'll make sure that they are fixed.
These challenge gc-codes has been found today:
GC78DFM GC7HP5Z GC7HTEZ GC7JQFT GC7KRYF GC7MBQ1 GC7JQFT GC7W7ZZ GC7Y544 GC8C5KK GC8PK92 GC1A3HC GC91DNA GC9392P GC906R3 GC9DDCV GC9MBK7 GC9N6RB GC9PAXE GC9PJ0Z GC798VD GC9YN6K GCA4MPW GCA4GNR GCA4T0H GCAA1QG GCAA1QM GCAA1QV