Good to hear from you again. You said in one of your other posts that your bees really don't experience winter, so I'd like to pose one possibility - opening up your outer cover to provide a little more ventilation is most likely not what would have done this colony in - I'd look elsewhere for other factors that may be dragging it down. A lot of us run our hives with the outer covers propped up a little, and our bees reach temperatures much lower than your'e encountering. Robbing, queen issues, and even nosema can cause issues in a hive, and are probably a little more in the direction that you might want to consider looking. I hope the solution presents itself though, and look forward to hearing more about what you find.
I think that laying worker situations will most often result in many eggs per cell, drone cappings rather than worker cappings, and I believe the eggs are often not anchored to the bottom-center of the cell, but rather inconsistenly located and sometimes on the sides of the cell. A drone-laying queen can also drag the colony down as well.
Some others will hopefully weigh in with better suggestions, but I wouldn't feel too bad about the outer cover thing - I think other factors are probably at the heart of this. Good luck and let us know what else you find.