Bracketing out, for a moment, the matter of the hatarot nedarim that everyone makes before Rosh Hashana and Yom Kippur, the text of the regular hatarat nedarim (annulment of vows) (http://halachipedia.com/index.php?title=Hatarat_Nedarim) includes a statement that all vows made in the next year are proleptically nullified--in addition to those from the last year, which are retroactively nullified. Should one take this literally, insofar as another failed vow made in that year would not require a new hatarat nedarim? Or should one make a hatarat nedarim anyway, i.e., in order to extend the stringency to the next year?
The answer is that for most cases hatarat nedarim is needed.
See Mishna Nedarim 23a:
R' Eliezer B. Jacob said: also he who wishes to subject his friend to a vow to eat with him, should declare: every vow which I may make in the future shall be null'. [his vows are then invalid,] providing that he remembers this at the time of the vow.
The Gemara gives a clearer of our Mishna (I don't want discuss here about the real nature of "The text is defective, and this is what was taught").
The text is defective, and this is what was taught : ... And he who desires that none of his vows made during the year shall be valid, let him stand at the beginning of the year and declare, 'every vow which I may make in the future shall be null. [his vows are then invalid,] providing that he remembers this at the time of the vow.
- Rambam states that a such declaration can be declared for more than 1 year, in Mishne Torah Haflaa, Nedarim, 2, 4 he gives for instance a declaration for 10 years.
- In Gemara we learn two opposed views on this Mishna. Abaye explain that if when he made the vow, he remembered the declaration, this means that he decided now to cancel the declaration (and the declaration cannot help against this vow). But if he does not remember the declaration, the declaration cancels the vow. Rava explains that if he remembered the declaration and made a vow and has not specified that he want to cancel the declaration, this is a sign that he said in his heart that the declaration cancels the vow already at time of vowing (some rishonim say he needs to repeat the declaration). But if he do not remember, the vow is not canceled by the declaration.
A part of Rishnonim ruled as Abaye and an other part as Rava. Rambam Haflaa, Nedarim, 2, 4 and Shulchan Aruch YD 211, 2 reports the both opinions but recommend stringency, i.e. not follow the first in its leniency.
- If the vow was pronounced forgetting the declaration, (I am not sure that a general declaration following a Nusach is good according to all Rishonim), and the vow was covered by the declaration, so it is canceled instantaneously. But SA said that we need to follow the stringency of the second opinion. So they need Hatarat Nedarim.
- But if the vow was explicitly mentioned in the declaration remembered and he said in his heart explicitly that he want to use the declaration to cancel the vow, it is canceled and no need to Hatarat Nedarim.
NoteAll the above is for a person which "Mitcharet Meykaro" (which regret entirely) but if it is not the case and there is a need to find a "gateway", a simple hatarat nedarim is not valide at all. See SA YD 228, 4 and 228, 7 . We learn in Mishna and Gemara that a lot of vow need an effort of reflexion in way to demonstrate that the Noder regrets his neder, without this effort, helped by a Chacham, the Noder cannot know if he regrets truly. So for such situation the standard Hatarat nedarim does not help. Additionally, most people read the Hatarat nedarim at high rate, without really thinking. May be that they don't understand what is said, so it is of very low value concerning vows.