I don't think I know the exact answers.
I do remember reading that the IOE numbers are not necessarily assigned in order.
For example, your number may be IOE09-15010000, and the next case received on the same date could be IOE09-16080000.
So don't think that your IOE group number all have the similar received dates or priority dates.
But over time, you should see each IOE group become more green approved.
So right now, the I-765 have more green than the I-485.
The yellow processing on the I-485, I assume, are those having completed the biometrics and "being actively reviewed".
The graphs only save the last 1-week of updates, so you can compare the number of green approved from a week ago to now to get an idea of any movements in your IOE group.
The earlier IOE numbers for the I-485 seem to have higher proportions of green, and again remember that the IOE numbers do not necessarily correspond to the receive dates.
Incidentally, if you look at the graphs on the computer, there is a pretty slick slider at the bottom to zoom in on certain ranges.
And as @grant2 says, it seems random.