Rashi on Exodus 16:1:1:
בחמשה עשר יום. נתפרש היום של חניה זו, לפי שבו ביום כלתה החררה שהוציאו ממצרים והצרכו למן, למדנו שאכלו משירי הבצק [משירי המצה] ששים ואחת סעודות, :
Summary: The Torah mentioned the date because until the 1st day of the 2nd month, they ate from the leftover matzot taken out of Egypt. Then, they ran out and needed the mahn
Numbers 9:1-3:
וַיְדַבֵּ֣ר יְהוָ֣ה אֶל־מֹשֶׁ֣ה בְמִדְבַּר־סִ֠ינַי בַּשָּׁנָ֨ה הַשֵּׁנִ֜ית לְצֵאתָ֨ם מֵאֶ֧רֶץ מִצְרַ֛יִם בַּחֹ֥דֶשׁ הָרִאשׁ֖וֹן לֵאמֹֽר׃
And the LORD spoke unto Moses in the wilderness of Sinai, in the first month of the second year after they were come out of the land of Egypt, saying
Numbers 9:3:
בְּאַרְבָּעָ֣ה עָשָֽׂר־י֠וֹם בַּחֹ֨דֶשׁ הַזֶּ֜ה בֵּ֧ין הָֽעֲרְבַּ֛יִם תַּעֲשׂ֥וּ אֹת֖וֹ בְּמוֹעֲד֑וֹ כְּכָל־חֻקֹּתָ֥יו וּכְכָל־מִשְׁפָּטָ֖יו תַּעֲשׂ֥וּ אֹתֽוֹ׃
In the fourteenth day of this month, at dusk, ye shall keep it in its appointed season; according to all the statutes of it, and according to all the ordinances thereof, shall ye keep it.’
I assume that by stating that in the 2nd year they ate the Pesach lamb and performed all the commandments that should go with it, it includes the commandment of eating the lamb with matzah and maror, as well, as stated in:
Exodus 12:8:
וְאָכְל֥וּ אֶת־הַבָּשָׂ֖ר בַּלַּ֣יְלָה הַזֶּ֑ה צְלִי־אֵ֣שׁ וּמַצּ֔וֹת עַל־מְרֹרִ֖ים יֹאכְלֻֽהוּ׃
And they shall eat the flesh in that night, roast with fire, and unleavened bread; with bitter herbs they shall eat it.
If they did everything completely, and they needed matzot, but, we see that they ran out of dough, how did they bake new matzot?
Or, is there a different way of understanding what occurred?