As I was reading Al Hanisim this year, something odd struck me "לְחֹדֶשׁ שְׁנֵים עָשָׂר" - the 12th month. What struck me was that this year is a leap year so we actually celebrated Purim in the 13th month Adar Sheini (bet). I am assuming that the year the purim story happened was not a leap year hence purim that year was in fact the 12th month. But if thats the case, what is the significance of mentioning לְחֹדֶשׁ שְׁנֵים עָשָׂר in Al Hanisim, it seems to imply Purim should be in the 12th month - which halachically is not so....?
Based on Why is Purim on Adar II during a leap year?, thanks @Yishai, I would like to add to my question -Why does the megillah emphasize "bi-Shloshah Asar le-Chodesh Shneim Asar" - that Purim was in the 12th month?