Continuing to count with a blessing in the event that one counted during the day:
If one forgot to count at night and counted during the day without a blessing, as explained above, then he has not forfeited the blessing and may thus continue to count with a blessing on the following nights. This applies whether one forgot to count the Sefira of the first night and counted during the day or whether one forgot to count the Sefira of any other night and then counted during the day. [Due to this it is customary in certain communities for the Chazan of Shacharis to announce the Sefirah after Davening, in order to save one who forgot to count the previous night.]
 Admur 489/24
So also rules: Terumos Hadeshen 37; Levush 489/8; Olas Shabbos 489/8; Chok Yosef 489/24; Mateh Yosef; Birkeiy Yosef 489/17; Nehar Shalom; Mamar Mordechai 489/9; Shalmei Tzibur 297/26; Zechor Leavraham 489/70; Chayeh Adam 121/2; Beis Oved 18; M”B 489/34; Kaf Hachaim 489/80
Other opinions: Some Poskim rule that in such a case one is to continue to count the coming nights without a blessing. [Peri Chadash 489] The Poskim ibid all negate his opinion.
 The reason: The reason for why a blessing may be said when counting on the following nights, is because even according to those opinions that rule that if one missed the counting of a day he has lost the Mitzvah, in this case they agree that he did not lose the Mitzvah by missing one night being that he counted that Sefira the next day. Thus even in their opinion the Sefira for this individual is considered “Temimos/complete” being that one is counting all 49 days. Now, although there are opinions that rule that the counting is only valid at night, and hence if one forgot to count at night he is not obligated to count during the day, and accordingly even if one counted during the day it is meaningless and does not help make up the previous nights missed count for the completion of counting 49 days. Nevertheless there are opinions that rule that even if one did not count at all an entire day, or many days that he can continue counting with a blessing on the other nights. [Admur ibid] In other words, although according to the joint opinions of invalidating the day count and invaliding the future count if one missed a day, one is no longer able to count, nevertheless since this approach is based on a dispute in two different points of its argument it therefore has the status of a Safek Sfeka, in which case we rule that not only must one continue to count, but he may even do so with a blessing. The Safek Sfeka is as follows: Perhaps the day counting is valid, and even if it is not valid perhaps each day is a separate Mitzvah.
Tzaruch Iyun from previous ruling: In 489/12 Admur rules that if one casually overheard the counting of another person, without any particular intent of being Yotzei or not being Yotzei, he is to repeat the Sefira without a blessing. Why is a blessing not allowed due to this case being a Sfek Sfeka of a blessing, as ruled in 489/24: The Sfek Sfeka is as follows: 1) Perhaps one must always count himself, as rules some Poskim in 489/1. 2) Even if one may hear someone else count, perhaps he must have intention to fulfill his obligation? Furthermore, in the case of Admur 489/12 a third doubt added, as it refers to one who heard the count by Bein Hashmashos, and hence perhaps it was not even night and he has not fulfilled his obligation according to all! Vetzaruch Iyun! Perhaps however one can answer that there is a difference between the forms of Sfek Sfekas in this case and in the case in 489/24 [as brought in Yoreh Deah 110-111, and ruled in Admur 438/9] that a Sfek Sfeka is only given value when the two doubts each come with a separate claim, and thus there are two different claims for why one may continue counting Sefira. When however both doubts are making the same claim, that one was already Yotzei the Sefira, then we consider it all one doubt, and rule Safek Brachos Lihakel. Thus in 489/12 that all the doubts create the single claim of “he was already Yotzei”, it does not help to remove the Safek Brachos Lihakel rule from implementation. However in 489/24 in which the doubts are two different claims [perhaps yesterdays count was valid and even if it isn’t perhaps today’s count is valid] we implement the rule of Sfek Sfeka which overrides the Safek Bracha Lihakel.
Tzaruch Iyun from Siddur: In the Siddur there are scenarios of Safek Sfeka in which Admur rules stringently that a blessing may not be said, despite the Safek Sfeka. [See Siddur regarding saying a blessing on a Tallis during Bein Hashmashos] In Toras Menachem 5719 pages 230-233 the Rebbe states based on this ruling that according to Admur in the Siddur we apply the rule of Safek Brachos Lihakel even by a Sfek Sfeka, and so writes Ketzos Hashulchan 7 footnote 3. Thus the questioned is asked regarding if the final ruling in this case should also change, and based on the Siddur one should rule that a blessing is not to be said? One cannot answer that which was said previously, that there is a difference between a Safek Sfeka which makes the same claim and a Safek Sfeka that makes two different claims, as in the case of the Siddur there are two different claims, perhaps the Mitzvah of Tzitzis applies at night, and even if it doesn’t perhaps it is not yet night. Vetzaruch Iyun!
 Admur ibid; Peri Chadash 489 based on Michaber 489/8; and so is implied from Setimas Haposkim [Kaf Hachaim 489/81]
 Kaf Hachaim 489/80