Related for Berakhot 7:6

These are the Berachot (blessings) which do not seal off with [the phrase] Baruch [Ata Hashem] (Blessed are You Hashem): One that blesses on the fruit, and on the mitzvot, Birkat Hazimun, and the last Beracha in Birkat Hamazon. Rebbi Yossi Hagelili used to seal off the last Beracha in Birkat Hamazon and [therefore] make it long.

The Beracha (blessing) for undiluted wine is Borei Pri Haetz (Who created the fruit of the tree) and it (i.e. undiluted wine) can be used to wash hands. [If] he added water into it, [then] the Beracha on it [becomes] Borei Pri Hagafen (Who created the fruit of the vine) and it (i.e. diluted wine) cannot be used to wash hands. [These are] the words of Rebbi Eliezer. And the Chachamim (Sages) say, “Whether this one (i.e. undiluted wine) or that one (i.e. diluted wine), the Beracha on it is Borei Pri Hagafen and it cannot be used to wash hands.”

Regardless if [a person that is leading the Zimun] said Nevarech (Let us bless) or if he said Barchu (Bless) we do not stop him [and correct him] for this. [Only] cavilers stop [the leader] for this! [A group] of twenty [people] can split up [into two groups of ten people], as long as not even one person gets excluded from the Zimun.