A pullet is a young hen. When they start to lay it takes a few weeks to work up to full-size eggs.
Bantams of course lay small eggs anyway.
"Blood" spots are actually little bits of the lining of the oviduct, and do you no harm at all if you don't mind them. They are not, as some people think, fertile eggs or growing chicks. Commercial egg producers should shine a bright light through (candle) each egg to find the ones with spots, so supermarket eggs should not have them.
I think there is a minimum legal size for commercial eggs, and this is why pullet eggs are not widely available -- they are used instead in food processing, cakes etc.