I took 3 courses in 2017 (Sep-Dec) and was given 3 months Part-Time credit on the T2202A. I also took 3 courses in 2018 (Sep-Dec) but was given 4 months credit on T2202A?

In 2017 I had taken 3 courses for one of the semesters and the T2202A showed I had 3 months of Part-Time (September to December). In 2018 I also took 3 courses for each semester but both semesters show 4 months of Part-Time (January to April, September to December). Why does my 2017 T2202A show 3 months while the 2018 T2202A shows 4 months for the exact same period (September to December)? Is this something I should ask my University to fix or is it not worth looking into?

Investors and rental owners

I'd suggest you report 2018 Tuition as shown on your T2202A. 

Since you attended during each of 4 months (September through December) it seems reasonable.