I don’t know if there was an actual change between Ulduar and Cata but with Cata they said that the old gods were dead dead abs that’s why the shattering actually happened there deaths harmed the planet and deathwing was just the tipping point.
The wow comic also made it rather clear that C’thun was dead dead but even while dead he could still effect things and Cho’gall originally went to revive him but couldn’t so just got a power up instead.