A hand written note by a "publisher of the good news" is an official document. The "publisher" is the official custodian of record of said document. Individual "publishers" would legally be considered agents of their local congregations and therefor agents of their international organization.
I can't tell you how many times I went out in the ministry an we ended up working the "not-at-homes" for the morning/afternoon/evening. The territory card holder would hand each pair of publishers a sheet of not-at-homes to work. Therefor the information is being shared, even if internally.
Looking back at this it gives me the creeps. I had 2 state prisons who's inmate population was considered part of the congregation's territory. There were about 50 inmates that were considered publishers and part of our congregation. When they would parole they were often welcomed with open arms right into our meetings. Those "not-at-home" records would make perfect "Burglarize these Homes" lists.