https://web.archive.org/web/20040307094152/http://www.wizard...
I believe, at the time the OGL v1.0 was written, the intention of irrevocablility was there.
>A: Yes, it could. However, the License already defines what will happen to content that has been previously distributed using an earlier version, in Section 9. As a result, even if Wizards made a change you disagreed with, you could continue to use an earlier, acceptable version at your option. In other words, there's no reason for Wizards to ever make a change that the community of people using the Open Gaming License would object to, because the community would just ignore the change anyway.
If it goes to court I bet this quote will be mentioned. They cannot say this and then in small print do the opposite after people have relied on it for two decades.