12 pm isn't past noon, it's noon.
12 am is past noon just as much as it is before noon.
So for 12 o'clock, choosing am or pm is arbitrary convention.
So it would make more sense to reverse them, to get a consistant row that starts with 1:
1 am, 2 am, 3 am, 4 am, 5 am, 6 am, 7 am, 8 am, 9 am, 10 am, 11 am, 12 am, 1 pm , 2 pm , 3 pm , 4 pm , 5 pm , 6 pm , 7 pm , 8 pm , 9 pm , 10 pm , 11 pm , 12 pm