I am playing around with this feature for the first time and find it interesting. I can get results using {Label Personal Letter}
I change the string to {Label Personal Letter WHERE Author ~ Athanasius} Knowing I have a letter from him found in the {Label Personal Letter} search and it does not show up.
Am I missing something? Is the tagging incomplete in this feature? I notice I have letters from Spurgeon that don't show up as well.