Installer.exe is no longer setting the RegDeployStatus registry after calling RegisterDeploy(). The purpose of this was to send a special evar42 ping to track the RegisterDeploy() pass %. It appears this stopped working correctly after the 8u20 msi redesign.
When tracking 1603/1606 errors, it's good to know how many of them are a result of RegisterDeploy failing. I've seen a bunch of jusched.log's from customers that indicate that it's failing often. But we won't know the true percentage until this is fixed.