It's more like they released GPT 6 Sol too early because they were under pressure and now they are releasing the real version. You cannot do anything more than minor post-training in a week.
It seems that 6.1 Sol is closely related to Astra. As for whatever 6.0 Sol was, it's anyone's guess. I'd speculate that 6.0 was just 5.6 with post training. It's possible however that it is the same model but with severe performance issues resolved so they bumped the version number.