A question arose concerning a person who counted the Omer incorrectly, and his fellow, who stood beside him, corrected him. For example, an individual said, "Today is the third day of the Omer," and the person standing beside him, knowing that this counting was done in error, tells him, "The sixth day." Does this statement – "The sixth day" – constitute a counting in its own right, such that the person has now fulfilled his obligation and thus cannot count that night with a Beracha?
Hacham Ben Sion Abba Shaul (Israel, 1924-1998) addresses this question in his work Or Le'sion (vol. 3) and rules that a person in such a case may, in fact, count the Omer with a Beracha that night. He explains the so long as one did not say the word "Hayom" ("today"), but merely stated the number of that night's counting, he has not fulfilled his obligation. Hence, the individual in the case described above, who merely said the words, "The sixth day," without specifying, "Today is the sixth day," is not considered to have counted the Omer.
Hacham Ben Sion arrives at this conclusion on the basis of a comment by the Taz (commentary to the Shulhan Aruch by Rabbi David Halevi, Poland, 1586-1667) regarding the similar case of a person who asks somebody which day he should count. The Shulhan Aruch (Orah Haim 489:4; listen to audio recording for precise citation) rules that in such a case one should not respond, "Today is such-and-such day" if he had not yet counted that night, because he will thereby fulfill the requirement to count the Omer, and will thus be unable to count later with a Beracha. The Taz clarifies that this Halacha pertains only to saying, "Today is such-and-such day." One may, however, simply state the number of that night's counting without saying the word "Hayom," because stating the number alone does not fulfill the obligation to count.
Hacham Ben Sion noted that this rationale can certainly be applied also in the case of somebody who corrects another person who counted the wrong number. So long as he did not explicitly state, "Today is such-and-such day," he is not considered to have counted the Omer, and may therefore count later that night with a Beracha.
Summary: If a person hears somebody count the wrong number of the Omer, and corrects him by stating the correct number, he may still count that night with a Beracha. So long as he did not begin with the word "Hayom…" ("Today is…"), and instead simply stated the number, he is not considered to have counted the Omer.
