This is historically correct. In 167BC Intercalaris began on the day after 23February and in 170BC it began on the second day after 23February. Varro, writing in the first centuryBC, says "the twelfth month was February, and when intercalations take place the five last days of this month are removed." Since all the days after the Ides of Intercalaris were counted down to the beginning of March Intercalaris had either 27days (making 377 for the year) or 28 (making 378 for the year).