Everything you said is correct. However, things have very recently changed or are in the process of changing reguarding the Louisiana Pine Snake. Memphis Zoo is the headquarters of the SSP and built, or is building, a new off-exhibit facility for breeding and research with funds from the U.S. Forest Service. The plan is to move all the snakes in other zoos to Memphis where I assume they will be DNA typed and matched into breeding pairs, then dispersed to just 4 zoos for breeding. If I recall correctlly, they are Fort Worth Zoo, Ellen Trout Zoo, Audubon Institute in New Orleans, and Memphis Zoo will retain some, with the goal to release the offspring back into the wild. I assume the reason for this is that the breeding and/or reinterduction was not very sucessful with these rare snakes spread out among several zoos. I don't know how far along they are in this process right now.
Here's a link to an article about it in the Memphis Buisness Journal
http://www.bizjournals.com/memphis/news/2016/06/07/zoo-plans-snake-breeding-center.html