Jews had taught about Purgatory before Paul was ever born and understood there was a place where people would suffer for what they’d done while alive even though they were not damned to Hell. Paul is explaining that an existing understanding is correct and still in place under the New Covenant, not adding anything new at all.
Is that indeed what Paul is explaining? Because that is not at all what the Scripture annalex quoted says. Paul calls himself a masterbuilder of this foundation, not merely a gopher. According to the grace of God that was given to him. It certainly sounds like something big had happened to me.