Back in 1978 we had an elder who came back from the two week elders school with information regarding the Kingdom Hall library. He claimed that the instructor said that only Watchtower publications should be in the KH library. I had attended the same school the year before and no such instruction was given. Having been the TMS overseer I had placed a number on non-Watchtower Biblical and historical reference works in the KH library. I guess I was pretty liberal for a JW back then as I placed Hugh J. Schonfield's "The Passover Plot" in the KH library.
Well this elder, claiming a mandate given him by the recent elders school, purged the library of all non-Watchtower publications. Fortunately there were several JW families who were more enlightened than the elder and they took in all the purged publications and were thankful to have them. I left the JWs in 1984 so I don't know if these families are still JWs.
However, a couple of years after the KH library purge a CO said that non-Watchtower publications of Biblical and historical value could be included in the KH library. Though I doubt that he would have approved of "The Passover Plot." But anyone who has served on the BOE knows there is always that hot shot elder who takes any instruction from the GB to the extreme.