Reference for Eruvin 7:7
נִתְמַעֵט הָאֹכֶל, מוֹסִיף וּמְזַכֶּה, וְאֵין צָרִיךְ לְהוֹדִיעַ. נִתּוֹסְפוּ עֲלֵיהֶם, מוֹסִיף וּמְזַכֶּה, וְצָרִיךְ לְהוֹדִיעַ:
If the food fell below [the required amount (see Mishnah 8)], he adds and assigns, and he need not apprise (them). [If he wishes to add of his own, even another kind (of food), which is not the same as that of the original partnership, he adds it and assigns it to them, and he need not apprise them of it. For since some of the first kind remains, he does not seem to be making an eruv ab initio. But if he adds of the original kind, even if it (the first eruv) were entirely depleted, he brings of that kind and assigns it to them and need not apprise them.] If (dwellers in the courtyard) were added to them, he adds (to the eruv) and assigns it to them, and he need not apprise them. [This, only when the courtyard has two entrances to two alleyways; for when they make an eruv with the men of one mavui they are forbidden to use the other, for which reason he must apprise them, lest they not wish to acquire (passage) on one side and lose it on the other. But if it has only one entrance to this mavui, for which they made a partnership in the beginning, he need not apprise them, for a man may be benefitted (even) when he is not present, and he may not be made to incur a loss except when he is present.]