Q. When is the yortzait of Moishe Rabeinu and when does the Chevra Kadisha make their seuda this year with double Adar? There seems to be some incongruity within the Chevros, since some do it on the first Adar and others in the second. What is Horav Miller opinion?
If it is on the second Adar, why is it that we read Parshas Tetzave which is meramez by the name of Moshe Rabeinu missing to his petirah and yortzait?

A:   On question 474 in this forum answering a similar query we wrote:
“ Remoh (O.H. 568: 7) quoting Maharil and Mahari Mintz, rules that in regards to a common yortzait, the custom is to fast on the first Adar. However, Bais Yisroel (92) maintains that the yortzait of Moshe Rabeinu is observed on the second Adar. His reasoning is based on Talmud (Meggila 13b) that relates the miracle of Purim to the yortzait of Moshe Rabeinu and since Purim is celebrated on the second Adar so is his yortzait. Hilchos K’tanos (2: 173) also maintains that it is kept on the second Adar since our sages teach that, Hashem fulfills the years of the just until the last day (Rosh Hashana 11a), if the year he past away was a leap year, it would have occurred on the second Adar. (See also Yaaros D’vash 2 p. 140 and Shilas Yavetz 1: 117))
Horav Shlomo Miller Shlit’a pointed out, that although it is custom for the chevra kadisha societies to fast and commemorate their traditional seudah on the seventh day of second Adar, Mishna Berura (580; 15) mentions that the fasting for Moshe Rabeinu’s yortzait is on the first Adar.”

Indeed, Imrei Pinchas (p.130) elucidates that Zain Adar should be commemorated on the first Adar, since it then coincides with Parshas Tetzave. As the Ba’al Haturim explains that Moshe Rabbenu’s name was omitted to comply with the “Erase me from Your sefer” dictum.
However, many Poskim maintain that Adar Sheni is main (Sheilas Yavetz 1: 117 quoting his father the Chacham Tzvi, Chasam Sofer O.H. 163, Melamed Lehoil 113,2, et. al.) Nitey Gavriel (Purim 13: 4) writes that some observe both dates.
There is a further disagreement of our sages as to when Moshe Rabbenu was niftar. If it was a year with two Adars and in which of the two was his petirah. (Yalkut Yehoshua ch. 5) as there is also a disagreement when he was born (Sota 12b.) There are also different opinions as to if he passed away on the same Adar he was born. (Hilchos K’tanos 2: 173, Ya’aros Devash 2: p. 140)

Horav Shlomo Miller’s Shlit”a opinion is that in principle each Chevra Kadisha should consult with the competent Rabbi in charge of the group and follow his opinion. When that is not an option, they should follow the already established minhag they have. If it is a newly created Chevra, they should follow the tradition of the majority of the established chevros in the city,

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a