I'm working on a GUI-based utility to speed up the creation of complex parts in KiCAD (I am aware of KiPart, hence the "GUI-based"). Anyway, I downloaded the largest BGA datasheet I could find for eventual testing. I found a Xilinx UltraScale FPGA with 2892 balls. What I noticed is that on the row/column grid, the labels 'I', 'O', 'Q', 'S', 'X' and 'Y' are missing and this also goes for when the labels double, so, for example, 'AO' is missing. Checking other datasheets for other parts from other manufacturers turns up the same results.
What I need to know is why this is, and if it is a standard, can I be directed to said standard? Is there ever a time where this will not be the case? I wasn't expecting this and it will complicate GUI creation a bit. I need to make absolutely sure that the GUI will match any datasheet on this issue.