Created an 2D array:
bigFloorLayout = []       
        bigFloorLayout=[[False for row in range(0,45] for col in range(0,70]


for y in range (offsetY, storageY + offsetY):
            for x in range (offsetX, storageX + offsetX):
                bigFloorLayout[x][y] = True

Offset is a negative number, and thus accessing bigFloorLayout[0][-1], which did not yield "Index out of Bounds" as it should.
This is in Blender 2.81, so I have no idea what version of python it is.

`-1` is not out of bounds unless the array is empty; negative indices count from the other end:

>>> a = list("some array")
>>> a
['s', 'o', 'm', 'e', ' ', 'a', 'r', 'r', 'a', 'y']
>>> a[-1]
'y'
>>> b = []
>>> b[-1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range



See about halfway down this [1] section; look for "Indices may also be negative".

[1] https://docs.python.org/3/tutorial/introduction.html?highlight=Indices+negative+numbers#strings

Ahh, thanks.