Riffing off of this: A better heuristic that can accommodate both the observation and necessity of change in how books are appraised could be: "What is the old

Riffing off of this: A better heuristic that can accommodate both the observation and necessity of change in how books are appraised could be: "What is the oldest possible correct book for the given topic, that continues to be read today?" If new books come for new topics that's fine, read them if the topic matters. Else older books might be better to use given the previous argument.