iStock has a clear, informative system to explain the ELs you get there. It's one of the features of their site which is really well done IMO. The only problem I have had with their system is that I don't get enough ELs

But when I get one I like how they tell me exactly what rights were sold, how much they charged, and how much I got paid. I just look at the list my ELs and click on each and a window opens which gives me the information.
It's been so long since I got an EL at SS that I don't remember how it works. Since they started ODs I have seen several people say that ELs have dried up. Maybe it's coincidence.