Regarding a person who is in doubt whether he said “vesein bracha” or “vesein tal umatar,” there is a chazakah that for the first 30 days, he said it wrong (and he must daven again).
My question is: Would it depend on the person? For example, if he is 95% certain that he said it right (such as one who davened from a siddur, which helps somewhat to avoid mistakes), would we say that he should not repeat, even if he cannot recall with absolute certainty what he said? Or if one knows that he personally becomes accustomed to saying it the right way within less than 30 days? Or a person who suffers from OCD and he constantly imagines that he said it wrong, even though he almost certainly said it right?
If one was cognizant of what he needed to say as he was davening, and only later in the tefilla or after davening started to doubt if he said the right way, he does not need to heed this doubt and does not need to repeat his davening. Only when close to the bracha he doubts what he said is the above halacha pertinent.
A person’s personal status will not change the halacha of 30 days.
Mishna Brura 114:38, the Mishna Brura is stringent only for one who was cognizant before tefilla but not during tefilla, that he must heed a doubt that arises immediately after davening. One who was cognizant during davening does not need to heed even such a doubt [this is clear form the sources the Mishan Brura bases himself on].
For someone suffering from OCD there is even more room for leniency, see here with the sources cited.