I got two consecutive bricks this week; APU4789000-999 (f74/b56) and 4790000-999 (f70/b70). These two bricks fits in the standard matrix for mini reams.
What is more interesting is that in the first brick (4789000), there was no replacements, but in the second brick (4790000), I found four replacements (APN0990800-802 replacing xxx260-262, and -827 replacing xxx804), with the same position numbers.
Moreover, a friend of mine got the next brick (4791000) and had replacements in the same places. I just regret to not having a brick in the 4796000-4800000 range to see if there is replacement in the same places...