If one passed away on the 30th of Marcheshvan, or the 30th of Kisleiv, when is the Yahrzeit commemorated in a year that there is only one day of Rosh Chodesh Cheshvan or Kisleiv?[1]
If the first Yahrzeit contains 29 days:[2] If one passed away on the 30th of Marcheshvan, or the 30th of Kisleiv, and the first Yahrzeit falls in a year that has only one day of Rosh Chodesh Cheshvan or Kisleiv, then the Yahrzeit is to be commemorated on the 29th of Cheshvan or the 29th of Kisleiv, on that year and annually. [This applies even in a later year in which Cheshvan or Kisleiv contains 30 days, nevertheless, it is commemorated on the 29th.[3] Nonetheless, Lechatchilah, it is proper to also keep the customs of the Yahrzeit on the 1st of Kisleiv/Teves.[4]]
If the first Yahrzeit also contains 30 days:[5] If one passed away on the 30th of Marcheshvan, or the 30th of Kisleiv, and the first Yahrzeit falls in a year that again has 30 days in Cheshvan or Kisleiv, then the Yahrzeit is to be commemorated on the 30th of Cheshvan or the 30th of Kisleiv, on that year and on each subsequent year that the month contains 30 days.
[1] See Kaf Hachaim 568:85; Piskeiy Teshuvos 568:12; Nitei Gavriel 77:9-10
[2] M”A 568:20; Taz 568:3 [although does not differentiate between when first year is]; Shaareiy Teshuvah 568:16 that so is custom; Chochmas Adam 171:1; Mateh Ephraim 3:7; Kitzur SHU”A 221:4; M”B 568:43 that so is custom;
Other opinions: Some Poskim rule one is to commemorate the Yahrzeit on the first of Kisleiv/Shevat in all cases. [Shaareiy Teshuvah ibid in name of Panim Meiros 2:83; Mamar Mordechai 10; Bigdei Yesha 568:22; Aruch Hashulchan 568:15; Igros Moshe Y.D. 3:153]
[3] Implication of M”A ibid; Mateh Ephraim ibid; Piskeiy Teshuvos ibid; Nitei Gavriel ibid
[4] Mateh Ephraim ibid; Kitzur SHU”A ibid; Kaf Hachaim ibid; Piskeiy Teshuvos ibid; Nitei Gavriel ibid
[5] M”A ibid; Kitzur SHU”A ibid; M”B ibid; Gesher Hachaim ibid; Piskeiy Teshuvos ibid; So rule regarding all years: Shaareiy Teshuvah ibid in name of Panim Meiros 2:83; Mamar Mordechai 10; Bigdei Yesha 568:22; Aruch Hashulchan 568:15; Igros Moshe Y.D. 3:153
Other opinions: Some Poskim rule that the Yahrzeit is to be commemorated on the 29th of Cheshvan/Kisleiv in all cases. [Taz ibid who omits the above differentiation brought in M”A ibid]