ELBO (Electronics Boutique, GMG's US nearest equivalent) which took a similar, if less pronounced fall on a similar warning, is showing early signs of recovery. It gained 6.82% yesterday on a flat day in the US - see:
I guess that investors in ELBO don't have a fixed date for an updated trading statement but are rather acting presumably on the unfolding evidence of improved sales in later-than-usual consumer activity as we seem to have experienced in the UK. Some GMG investors will wait until the 10th before committing, perhaps explaining the much more gradual rise of 1% or 2% per day.
As for GMG's price on Jan 9th, I don't personally care what unrealistically low valuation is still seen by then since I don't anticipate any material move back northward to more realistic levels until the market digests the data in the trading update (when hopefully the scale of December's over-reaction is acknowledged).
The party - or the wake - starts on the 10th. And I don't anticipate wearing black on that day.