(Note: Left Behind recommends having had completed the campaign of The Last of Us before starting Left Behind, as such, assume the same here.)
Just a quick note. It took Naughty Dog - the developers - until the PS3 was nearly dead, and on gamer's shelves, to publish a single player DLC for one of there games. This speaks to how special Left Behind is. It is not a last minute cash grab or a Capcom like locking out of content on the disc. This is a story that came to light after finishing the main title and talking and deciding, this is a story worth telling.