'Cut off cuts doesn't mean it's for him'

In the Gemara in Kiddushin (5:1), a sermon by Rabbi HaGalili is presented based on the verse "And he wrote to her a book of cuttings," which was to be written in the verse "Sefer Keret," and it was found that the box "keret" contains a lesson. From this, Rabbi HaGalili learns his sermon. However, for the sages, "keret keret" does not mean "he." I searched for a little explanation for this. That is, why do the sages really not see this as an exception (after all, the verse should only be written "keret"). And on the other hand, why does Rabbi HaGalili see this as an exception – and that is, what are the sides of the disputes and opinions? I did not find any mention of this. Do you know anything to add to this?