I added a new field to the spreadsheet. A simple yes/no question regarding whether or not you're IV breeding, in case IVs are still used to calculate a Pokemon's shininess.
The reason I added that is because I noticed that when I bred pokemon that were less than perfect with my 6IV Japanese ditto, I got a shiny on the 16th egg, and the 43rd egg. I don't know if this is just a coincidence or not. Also, Crisc got a shiny beldum on his 5th egg, doing something similar.
I also noticed a pattern in my breeding. My first shiny was after 543 eggs, but after that I got one in 16. Then I bred around another 500 or so for my magikarp, then 43 eggs into a torchic, a shiny one comes out. So, I'm guessing that my honedge will take somewhere past 500 eggs to hatch, based on the current pattern. If anyone else is experiencing similar patterns, let me know. I might just be getting really lucky