Here are a couple of articles about blood and meat spots in eggs:
https://www.theprairiehomestead.com/2013/02/what-are-those-spots-in-my-farm-fresh-eggs.html
http://www.thepoultrysite.com/publications/1/egg-quality-handbook/29/meat-spots/
https://www.theprairiehomestead.com/2013/02/what-are-those-spots-in-my-farm-fresh-eggs.html
http://www.thepoultrysite.com/publications/1/egg-quality-handbook/29/meat-spots/