The meaning of the words "l'Shanah Acheres" seems to be related to another basic question on the Gemara: How could it be that Shmuel ha'Katan -- who was the one who instituted the blessing of Birkas ha'Tzedukim -- forgot the words of the blessing? In addition, how could it be that every person in the entire congregation also forgot the blessing, such that no one was able to remind him of the words, and they all needed to wait three hours for him to remember it? (See Rashba.)

(a) Rav Yakov Emden suggests that Shmuel ha'Katan did not usually recite the full Shemoneh Esreh (due to his constant involvement in Torah learning; see Shabbos 11a), but rather he recited the shorted "Havinenu" prayer. Since he did not recite the Shemoneh Esreh except when he was the Shali'ach Tzibur, he forgot the text of the blessing. We may add that there are sources that permit a person who is entirely involved in Torah learning to forego Tefilah with a Minyan in order not to cause an interruption in his learning (see Rashi to Chulin 133a, DH Ansei). This would explain why Shmuel ha'Katan did not hear the blessing recited by the Shali'ach Tzibur, as he did not attend the Minyan regularly.

(b) The Yad David suggests that at the time of the original enactment of Birkas ha'Tzedukim, it was not commonly said in the individual Shemoneh Esreh. We know that at that time they did not use printed prayer books, but rather they recited the prayers by heart, and those who did not know the prayers by heart would listen to the Shali'ach Tzibur and fulfill their obligation through "Shome'a k'Oneh." Even Shmuel ha'Katan, who instituted the blessing, did not recite it in his individual Shemoneh Esreh (the Yad David suggests that the original enactment was made only for the Shali'ach Tzibur's Shemoneh Esreh and not for the individual's Shemoneh Esreh). Consequently, since he did not serve as Shali'ach Tzibur frequently, he forgot the words of the blessing the next time he served as Shali'ach Tzibur. This is what the Gemara is alluding to when it says "l'Shanah Acheres" -- it is explaining how Shmuel ha'Katan could have forgotten the blessing.

The Yad David, though, questions this approach, because it is still unlikely that Shmuel ha'Katan -- whom the Gemara says was worthy of prophecy -- would forget his own composition. Moreover, even if he did not recite it himself for a year, he certainly heard it from the Shali'ach Tzibur.

(c) The Pnei Yehoshua suggests further that when the blessing of Birkas ha'Tzedukim was enacted, like all other blessings it did not involve solely the composition a few words. Rather, it involved lofty Kavanos, intricate and deep calculations of words, letters, and their relationships to the various levels of the Kabbalistic concepts, and it necessitated the proper thoughts and intentions in order to bring about an effect in the higher worlds (see also Chida in Pesach Einayim). Shmuel ha'Katan certainly remembered the words that he composed, and many of the Kavanos. However, since he did not recite it in his individual Shemoneh Esreh, and since he did not serve as Shali'ach Tzibur daily, he was unable to recollect all of the proper Kavanos that were necessary to ensure that the blessing would have its desired effect in the upper worlds.

Accordingly, it is easy to understand why no one else who was present was able to remind him of the blessing -- no one else knew the deep Kavanos that were required. Also, this explains why it took three hours to remember. He didn't merely stand there, twiddling his thumbs and waiting for the words to pop into his head. Rather, he was standing in deep concentration, meditating on the holy Kavanos of the blessing.

As far as why Shmuel ha'Katan served as Shali'ach only once a year, perhaps there was some custom to be the Shali'ach Tzibur once a year, perhaps the custom of Yahrzeit, or a precursor the custom of Yahrzeit. I found no one who discussed this particular point.

Y. Shaw