Just to be clear, are you asking about upgraded boarding positions you get free with Southwest credit card?
That's not EB exactly
At least not as I have used it personally. What I have with the credit card is when I check in, if I get a late boarding position, I pay for A1-15 boarding and that gets refunded.
I've never seen them offer free EB as in what you buy when you buy your ticket (if that's what you are asking about)
It's 2 different things. Now they may offer free EB and upgraded boarding both, I'm not sure.
I just want to be certain you purchase the right thing based on what is offered free