I believe that although they did not specify, I am certain the length of break between consecutive stay is important.
So in your case you say your longest stay was 3 months. If the time between the next stay and the 3 months stay was greater than 6 months it will not be counted as continuous. But if after three months you left the country for a quick visit of 2 days and came back and continued to stay, the duration of the subsequent stay would he added to the original 3 months.
So to conclude, if you stayed outside Mexico for at least 6 months after your 3 month stay you definitely do not need it. But if you stayed outside for less than 6 months, you maybe asked for it, we cannot be sure, so better to get it.