My Asian friend had some old rootbark, cut in small pieces (not quite shredded but somewhat) sitting around for 3+ years (from MJB) before he finally felt like doing an extraction. It was his first, and he had done a poor job at cutting up the bark since his blender couldn't handle it. He did Noman's and got 0.3% (300mg from 100g bark). I blame the slightly below average yield on the large size of the bark pieces, not the age of the bark.
I've read though that freezing and thawing could help damage and break the cells; you could try it for this reason but nothing will happen to the spice in his bark if its just sitting a few weeks. I can't comment on leaving the acidified solution sit a few weeks but personally I wouldn't, and not only because I don't do this stuff, but I mean because molecules like to dance, who knows what can form after a few weeks of high-proton action. Probably nothing, but eh. Just tell him to seal the bark in a bag and put it in a dark cool drawer.
"He heard pre-shredded bark can go bad quick" its just a rumor which is probably false, unless the stuff is thrown out in the hot sun for a long time or something.
Shredded should be fine. What my friend who lives on an island does, is after the acid soaking and decanting, after the last soak, he wraps the bark in cheesecloth for easy grip and filtering effect, and squeezes very firmly