In Dayeinu, there are a few stichs which make no sense: how can we say "it would have been enough" without these promises, when Hashem already promised that He would have given them long before we even left Mitzraim?
אִלּוּ הוֹצִיאָנוּ מִמִצְרַיִם וְלֹא עָשָׂה בָהֶם שְׁפָטִים, דַּיֵּנוּ.
If He took us out of Mitzraim and not done judgements in them, it would have been enough for us.
Yet Hashem already promised to punish the Mitzri'im (Bereishis 15:14):
וְגַם אֶת־הַגּוֹי אֲשֶׁר יַעֲבֹדוּ דָּן אָנֹכִי
And also the nation which they will serve I will judge.
אִלּוּ עָשָׂה בֵאלֹהֵיהֶם, וְלֹא הָרַג אֶת־בְּכוֹרֵיהֶם, דַּיֵּנוּ.
If He made [judgements] on their gods and not killed their firstborn, it would have been enough for us.
Yet Hashem already promised to kill their firstborn (Shemos 4:23):
וָאֹמַר אֵלֶיךָ שַׁלַּח אֶת־בְּנִי וְיַעַבְדֵנִי וַתְּמָאֵן לְשַׁלְּחוֹ הִנֵּה אָנֹכִי הֹרֵג אֶת־בִּנְךָ בְּכֹרֶךָ׃
And I say to you, 'Send My son and he will serve Me,' yet you refuse to send him; behold, I [will] kill your son, your firstborn.
אִלּוּ הָרַג אֶת־בְּכוֹרֵיהֶם וְלֹא נָתַן לָנוּ אֶת־מָמוֹנָם, דַּיֵּנוּ.
If He killed their firstborn and not given to us their money, it would have been enough for us.
Yet Hashem already promised to give us Mitzraim's loot (Bereishis 15:14):
וְאַחֲרֵי־כֵן יֵצְאוּ בִּרְכֻשׁ גָּדוֹל
And afterwards, they will leave with much wealth.
אִלּוּ נָתַן לָנוּ אֶת־הַשַׁבָּת, וְלֹא קֵרְבָנוּ לִפְנֵי הַר סִינַי, דַּיֵּנוּ.
If He had given to us Shabbos and not brought us before Har Sinai, it would have been enough for us.
Yet Hashem already promised that we would come to Har Sinai (Shemos 3:12):
וְזֶה־לְּךָ הָאוֹת כִּי אָנֹכִי שְׁלַחְתִּיךָ בְּהוֹצִיאֲךָ אֶת־הָעָם מִמִּצְרַיִם תַּעַבְדוּן אֶת־הָאֱלֹהִים עַל הָהָר הַזֶּה׃
And this will be the sign to you that I have sent you: When you take the people out from Mitzraim, you will serve Hashem on this mountain.
אִלּוּ נַתַן לָנוּ אֶת־הַתּוֹרָה וְלֹא הִכְנִיסָנוּ לְאֶרֶץ יִשְׂרָאֵל, דַּיֵּנוּ.
If He gave to us the Torah and not brought us into Eretz Yisrael, it would have been enough for us.
Yet Hashem already promised to give us Eretz Yisrael (Bereishis 13:14-17):
שָׂא נָא עֵינֶיךָ וּרְאֵה מִן־הַמָּקוֹם אֲשֶׁר־אַתָּה שָׁם צָפֹנָה וָנֶגְבָּה וָקֵדְמָה וָיָמָּה׃ כִּי אֶת־כָּל־הָאָרֶץ אֲשֶׁר־אַתָּה רֹאֶה לְךָ אֶתְּנֶנָּה וּלְזַרְעֲךָ עַד־עוֹלָם׃ [...] קוּם הִתְהַלֵּךְ בָּאָרֶץ לְאָרְכָּהּ וּלְרָחְבָּהּ כִּי לְךָ אֶתְּנֶנָּה׃
Raise your eyes and see from the place where you are there – north, south, east, and west – for the entire land which you see, to you I will give it, and to your children forever. [...] Get up, walk in the land to its length and its width, for to you will I give it.
Unlike, say, giving the mann, Hashem had already promised to do these things long before they actually happened. The mann was only promised in response to Bnei Yisrael requesting food; all of these things listed above were not in response to a need for them, and were in fact promised long before they actually happened (by several centuries in some cases). How, then, can we say "it would have been enough" if Hashem didn't fulfill His promises?