If a congregation forgot to say birkas hachodesh on the Shabas before rosh chodesh, should it say it another time? When? (Does it, perhaps, depend on what day(s) of the week rosh chodesh is?)
Note: AFAICT, Shaare Efrayim and Mishna B'rura say nothing about this.
The Sefer Ishei Yisroel on Tefila says as follows, and brings as its source the Mekor Chaim end of Siman 284. If the Sefer Torah was returned to the Aron Kodesh, so long Shemona Esrei has not begun, you may still do Birchas HaChodesh, however it would be preferrable to say it at Mincha after Kriyas HaTorah prior to returning the Sefer Torah to the Aron Kodesh.
Rabbi Avigdor Nebenzahl, in his footnotes to Mishna Berura entitled ביצחק יקרא, writes in the first footnote to OC 417:
אם שכחו ולא אמרו ברכת החדש בשבת רשאים לומר ביום חול.
If they forgot to say Bircat haChodesh they are allowed to say [it] on a weekday. (my translation)
The Rivivos Efraim (OC 4 Siman 53) writes that they should not say it later publicly on a weekday, but the individuals can say it on their own during the week if they did not say it on Shabbos.
