If they've been refrigerated the entire time the "float test" will tell you which eggs have lost the most moisture, but it won't necessarily tell you if the egg is unsafe to eat.
The longest I've ever personally kept eggs in a refrigerator was four months. The yolks were mighty thin and the whites very watery, but they were not spoiled. That last month or so they'd have floated for sure they'd lost so much moisture. These were eggs that were clean out of the nest, never washed, and promptly refrigerated. Not the sort of thing I'd ordinarily do but I was going to be without birds for a time so we saved every egg we could to forestall having to buy eggs.
The Mother Earth News Magazine did some research on egg preservation. Of all the methods they tested (the traditional ways) they found that nothing worked so well as simple refrigeration. I seem to recall they got them to keep something like five or six months. Quality was pretty bad, but they were still safe to eat.