Kozhiglover on katan who becomes bar mitzvah during sefirah

There is a lot of discussion in Achronim regarding a katan who becomes bar mitzvah in the middle of sefira.  Can he count as a gadol with a bracha, or did the count he did as a katan not count (pardon the pun) for anything and it is as if he missed days? 

The Kozhiglover has a wild chidush.  He draws an analogy to the din of ben sorer u'moreh: The gemara (San 68b) brings proof from a pasuk that a katan not close to the age of maturity is exempt from the din of ben su"m.  Asks the gemara: why do we need a pasuk here?  A katan is patur from all mitzvos?  Answers the gemara: ben s"um is a special case since he is "ne'herag al shem sofo," he is being penalized because he will grow up into a rasha, so one might have thought there is no bottom age limit, kah mashma lan there is. 

 קטן מנלן דפטור מנלן כדקתני טעמא שלא בא לכלל מצות ותו היכא אשכחן דענש הכתוב דהכא ליבעי קרא למיפטריה אנן הכי קאמרינן אטו בן סורר ומורה על חטאו נהרג על שם סופו נהרג וכיון דעל שם סופו נהרג אפילו קטן נמי 

The gemara is not saying that viz a viz hilchos ben sorer u'moreh the age of maturity is 12 3/4 or so, like we find by the din of mufla ha'samuch l'ish that tells us that viz a viz hil nedarim the age of maturity is 12, not 13.  Were that the case, the hava amina would make no sense -- why would every katan be included?  The gemara is saying that since neherag al shem sofo, there are consequences that will come out when the child becomes a gadol, the child is subject to onshim even as a katan, even below the age of maturity.

By the same logic, argues the Kozhiglover, since whether or not the katan counts has consequences viz a viz his ability to continue counting sefira as a gadol, he becomes mechuyav as a katan.