…it turns out to be (I know this will sound ridiculous) the limitation of dimensions to the 10,000th of an inch. 
Don’t back hand me just yet… hear me out.
As I was prepping the intersecting lip for joinery by way of notching, I discovered why doing this in the past has been with challenging result. I will illustrate with an example:
If setting out to joint these two sides together with notches, first I take my material thickness into account: .23" and draw a box for that dimension:
Then I decide that I want 1" notches, so I duplicate the shape and divide its width by 16:
With the array tool, I now create my notch segments:
It works out fine:
Its when the base object isn’t an even number like the example with 16" of width. When working with a width such as this I divided it by 16 (and there lies the problem, the quotient from the first divisor as the result was .9786):
So the resulting array did the math as it should (.9786 * 16 = 15.6576). But that is now longer than my original.
I understand, the width and height appears to be capped at a resolution in the 10,000ths. And it seems rational and adequate. I always thought so. But this is at least one example where it can show itself. You know, maybe it won’t even make a difference. I’ll make the pieces and report back. I’ll probably have more of a challenge with my own laser kerf than 8/10,000 of an inch.
