What would a PIMI define as "old"? That refers to a anything not in the present. Yesterday is old (i.e. day old bread).
Is there an expiration date on Watchtower literature like there is on a carton of milk? At what point is it no longer safe to read a particular book or magazine that was published by the Watchtower?
If I drink expired milk I risk getting food poisoning and getting physically ill. What risk do I take from reading old literature?
The Bible was literally written thousands of years ago. Should we stop reading it since it is no longer safe to read a Watchtower publication based on the Bible that was written a decade or two ago?
If there is something wrong with reading a Watchtower publication today, why was it considered required reading by the entire organization at the time it was printed? Why was the release of that publication literally celebrated with thunderous applause at a convention?