So, I said that I was going to run a test to see if SWA changed our Early Bird assignment if I changed our ticket for a lower priced one at some point after the original purchase. My husband and I have separate SWA accounts and I bought our tickets and added Early bird at the same time. Then some time later, prices dropped and I only changed my husband's ticket and not mine.
Well, the results are in and not very clear. We got our position assignments for tomorrow's flight and mine is A46 and my husband's is A48, so not sequential, but very close. I also purchased my EB six minutes before I purchased his, which could explain the slight gap in numbers.