They might have been thinking of this:
*** km 1/89 p. 7 Question Box ***Although a brief announcement concerning a wedding scheduled to take place in the Kingdom Hall may be made at one of the meetings, a formal wedding announcement would not be placed on the information board. Neither would it be proper to post announcements about gatherings of a strictly social nature, since these are not related to congregation activities.—See TheWatchtower, April 15, 1984, page 15; KingdomMinistry, June 1975, page 4, and May 1970, page 8.
*** km 5/70 p. 8 Question Box ***The information board is not to be used for personal items such as "shower" announcements.
I can see why some jws would not want the reception info posted if they are doing it by invitation only. Also, some jws might be trying to save money by having that info posted rather than sending invitations. I'm not saying anyone here had that motivation, but I can see some elders "reasoning" that way.
Blondie