I can't find mention of this anywhere [not that I've been looking long], but I can't be the first to point this out about the Powell photo.
Below is an extreme close-up of the SN window and the boxes forming the SN. Note, there is a box that is higher than the rest. To the left of this box as we look at it [to the west of the highest box], there are at least two stacks of boxes.
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However, the picture below shows that there is only one stack of boxes to the west of the tallest box:
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This is the same arrangement as we see today in the 6th floor museum:
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Am I missing something really obvious because it looks to me that at least one stack of boxes is missing from the Sniper's Nest as pictured in the Powell photo?