At day 7 it's not a speck. It's probably 1/2 inch and rocking quite a bit. Maybe you're just looking at the eye not the full embryo? I'll dig through my photos to see if I have a good picture.I took the pictures in a room where I brood my chicks. Sure it wasn’t totally dark because the chicks like to have a night light. But even in your pictures of the day 7 egg you can see only a small speck. More of the egg is taken up in my pictures. Ambient light or not. Tonight when it is totally dark I will make it totally dark and get better pictures. But the eggs are not see through like your day 7 pictures.
But if you say the veining is day 7 then how come the chick takes up so much space?