How would I troubleshoot generic icons for apps showing in a third party app?
Well - it turns out LaunchBar was reporting things as they are and Finder and the rest of the systems started dropping the icons to match what this utility was showing.

I have recovered from the failure by rebuilding the launch services database.

The short command is lsregister -kill -seed and here's the full path

  /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -seed


This still hasn't figured out why they went wrong, but it's a rebuild step that can be taken once the number of "broken" icons become aggravating. This is very odd to me since the lsregister command used to be vey handy when duplicate open as records were present, but I didn't have that symptom here. Also, typically cleaning icon caches in /var/folders and then performing a safe boot. That's not something I ever liked contemplating and was very happy to not have to resort to trying that in this case.