That is really interesting I have always said that my eggs stored in the fridge will keep a while but OH who is a townie is always worried, he is getting better as at one time he wouldn't eat anything out of the garden and he thought I didn't notice
It won't be the same now but a few decades ago we worked out that eggs you bought in the supermarket would have been laid
six weeks earlier. So I reckon my eggs will always be fresher than supermarket ones, even if I have just found a nest of 20 eggs I had no idea existed...
Plus if there is any doubt at all I break them onto a saucer - if the egg is on the way past its best before date, the yolk will not stay in a nice round globule. So that'll be one for the dogs, or cat.
There is another test involving dropping the egg into water, it sinks or floats but I can never remember which way round it is - plus you have to make sure the water is warmer than the egg or you push any germs on the shell into the egg. So I just use the break-onto-saucer technique (and don't use eggs I am not certain about for boiling in their shells
.)