Well, it is very possible that WOTC altered the 4E GSL "at will" for Goodman because he asked nicely and at the right time.
OR he could be doing it under copyright laws before October 1, and then going GSL by October 1. It isn't like Goodman would be violating the GSL by doing that. Plus I doubt it would upset WOTC. They would applaud his savvy and take note of it for their next license. Then welcome him to the GSL family.
Certainly, but at that point it's no longer the GSL, it's a separate agreement between Goodman and WotC. Once you relax the one restriction it's no longer the same contract.
It sounds like nit picking but it's not. It could be the case that it's a special agreement that is identical to the GSL save for the release date clause, I'd say that's unlikely though. If you take the position that GG negotiated a separate licensing agreement it seems unlikely that the only thing they'd want changed is the release date. It's certainly possible though, since GG may highly value the ability to release early at Gencon.
But what we know is this: it is not the GSL. It absolutely cannot be because of the release date clause. The consequence of that is that the other things that are occurring (sellling off the 3e stock) can't be used as evidence of ... well anything really. We're all just guessing... not that there's anything wrong with that.
If it were me, and I were trying to run a business based on 3rd party D&D material I would completely ignore the GSL and try to negotiate a separate contract. Paying royalties for some of the restrictions to be relaxed, particularly in the area of what stat blocks can be included, would be a small price to pay.
As an aside, for my stuff, which I'm not trying to base a business on, the GSL is fine. I wouldn't be the licensee directly I don't think. So I suppose I better figure out how to form a company that can legally sign up.