Twenty years ago, before all the mites came along, and forced, or let me say "encouraged" beekeepers to play around with this or that, hive loss was almost NOTHING. And yet, I talk to people from those years past, and none of them provided top entrances unless they bought or acquired inner covers with notches. And most of them that did have notched inner covers, sealed them. I have bought inner covers from guys going out of business, and many had the notches filled or blocked off.
Yeah, someone, somewhere, always will promotes this or that, and I'm sure someone can dig up an old BC or ABJ article about top entrances and moisture perils. But how did beekeepers 30 years ago, keep almost all their hives alive, and yet so few of them used top entrances? I'll tell you why....because this whole thing has been way overblown by a few, who seem to feel that if you do not have an top entrance, the hive will die. No way!
My hives that have upper entrances, the bees block 50% of them off. If it is the only entrance, bees will sometimes close them smaller but will not close them off. If the bees have other entrances, many will close off an upper entrance. I see no difference in hive kill between those that have upper entrances and those that do not.
Now can a beekeeper do things that will cause an unnatural amount of moisture in a hive? Sure, like feeding syrup way too late in the season, and thus not allowing bees to process it correctly. But that is an example of not doing the correct thing to begin with, then continuing a second manipulation to offset the first one. Quit feeding syrup in the late fall and throughout winter, and almost ALL moisture concerns are eliminated.
A healthy hive, not filled late season with syrup which causes huge moisture problems, will not perish due to moisture in the absence of a top entrance. If that was true, many hives prior to mites would of perished due to so many NOT having top entrances. That was not seen then, and I do not see it now.