The film keeps really well honestly. All the Fuji instant stuff keeps far better than Polaroid. For whatever reason they are getting a much better seal on their pods. Also, the color shifts are much less. I shot 9 year old Instax film and every shot covered completely. There was a slight color shift but nothing like the orange cast and lack of contrast that ruined Polaroid 600 shots.
Remember that the ISO 3200 is actually an ISO ~1000 formulation with a reflective back layer to add to the sensitivity. So it isn't nearly as sensitive to age as real ISO 3200 film.
Umm real "ISO 3200 film" is also actually 1000 that pushes well....
Also, so that's what the white backing is? It reflects light back onto the film for added intensity?