How I heard it, someone would get something smuggled in page by page or less often, one (1) whole magazine and it would get copied down so more people could 'benefit' from the 'spiritual riches' coming from the zealots of Brooklyn.
I recall one experience told about Eastern Europe, where sister's would bring walnuts in a basket to the JW prisoners in jail. (Obviously, where this was allowed). The top ones were real in case the guard helped himself. The bottom ones had been carefully opened with their meat extracted and a page from a Watchtower tightly rolled up, stuffed in, and the two shells glued back carefully together.
LL
PS I appreciate this topic so I can clean that corner of my brain out from worthless information.