Yes, it's a bit counterintuitive with the opened concentrate going bad faster than mixed replenisher. Kodak are very clear that opened concentrate will not keep, hence mixing up bags of replenisher and working your way through it. Obviously if you don't protect the replenisher carefully it will go bad too, but the consensus on APUG is that replenisher keeps far longer than open concentrate.
Unopened concentrate will still only last a couple years from manufacture since the CD4 (or whatever it is) decomposes even without oxidation. But that's a cheap part.