The text of Hataras Nedarim says just the opposite; after listing various types of Nedarim from which the asker seeks exemption, he adds:
הֵן אוֹתָם הַיְדוּעִים לִי, הֵן אוֹתָם שֶׁכְּבָר נִשְׁכְּחוּ מִמֶּנִּי, בְּכֻלְּהוֹן אִתְחֲרַטְנָא בְהוֹן מֵעִקָּרָא, וְשׁוֹאֵל וּמְבַקֵּשׁ אֲנִי מִמַּעֲלַתְכֶם הַתָּרָה עֲלֵיהֶם
...whether those which are known to me, whether those which are already forgotten from me: regarding all of them, I regret them retroactively, and I ask and seek from your eminences exemption from them.
What you seem to be remembering is the opposite case - that if one vows without recalling the conditions of his most recent Hataras Nedarim, the vow is null and void retroactively; to quote the text again, this time from the final paragraph:
וּבְאִם שֶׁאֶשְׁכַּח לִתְנַאי מוֹדָעָה הַזֹּאת וְאֶדּוֹר מֵהַיּוֹם עוֹד, מֵעַתָּה אֲנִי מִתְחָרֵט עֲלֵיהֶם וּמַתְנֶה עֲלֵיהֶם שֶׁיִּהְיוּ כֻּלָּן בְּטֵלִין וּמְבֻטָּלִין, לָא שְׁרִירִין וְלָא קַיָּמִין, וְלָא יְהוֹן חָלִין כְּלָל וּכְלָל. בְּכֻלָּן אִתְחֲרַטְנָא בְהוֹן מֵעַתָּה וְעַד עוֹלָם:
And if I forget the conditions of this declaration, and I vow from this day onwards, from now do I regret them and make a condition of them that they all be null and void, not binding nor lasting, and that they never come into effect. Regarding all of them I regret them from now until forever.