I purchase whatever is on sale (Simply Orange, Florida’s Natural, Tropicana). I’ve never seen the “Passover” seal on any national brand of Orange Juice.
Simply Orange is a product of the Coca Cola Company. It is a highly engineered product. Here’s a link to an article discussing how it is manufactured:
http://chicagoist.com/2013/02/10/simply_orange_is_anything_but.php
Coca-Cola only sells Kosher for Passover Coke in neighborhoods that are heavily Jewish around here - I have to drive a bit and search out a store that has it if I want it. Perhaps the originally poster ventured into a Goyim neighborhood.
Kosher for Passover Coke uses real sugar instead of Corn Sugar. Maybe something similar in play here. But 777 seems eager to throw that victim card.
In purchasing whatever is on sale, you might want to check the label. Sometimes, the product originates outside the country. I prefer for our food to come from the USA.