Does my manager have to follow written documentation when determining discipline?

I work in Illinois. Attendance policy is 5 occurrences per calendar year before disciplinary action is taken, managers decided what is excused v unexcused. At 6 you are given a verbal warning, 7 written, 8 final written, 9 termination. Occurrences reset on 1/1 of each year, but disciplines are active for 12 months.

I got a signed, certified letter on Day 5 stating that Day 1 and Day 2 are unexcused, I have 4 unexcused absences for 2019.

I took a leave originally starting on Day 3, but moved back to Day 1, child was born on Day 1 so Day 1 and Day 2 were excused by the leave. Fast forward to my return to work. I missed an additional 2 days, now I am being advised I am at 6 absences and received a verbal warning. Shouldn't my manager have to honor her written signed, certified letter stating I had 3 before my leave? (Letter dated day 5 says, day 1 and 2 are unexcused, I am at 4 unexcused. Now since day 1 and 2 are excused, I would take the letter to mean I have 3 unexcused.) I am concerned this is more retaliatory than anything else, so I see this ending in termination and I want to make sure I have an understanding of what is going on before it gets that far.