"...the stuff I labeled lutzi could be called cf. lutzi. I've only seen one collection of lutzi, the types from Sao Paulo. So I don't know what variation is like. But your specimens are almost exactly in between lutzi and auropunctata. The workers are nearly identical to auropunctata except with petiole shape of lutzi. The queen is bigger than auropunctata, but the shape of the head and frontal carinae are like auropunctata instead of lutzi. I bet it is an undescribed species."
And as I recall my issue with (what I thought was) sigmoidea was that they seemed a lot like auropunctata except for that petiole, so actually that seems like a reasonable mistake for me to have made. The critical couplet is the one which involves the antennal scrobes being narrow or broad. If this key ever gets published, I would caution folks to be especially careful on that couplet.
The auropunctata (workers), iheringi, and scrobifera were all correct and pretty easy to ID. I'm guessing that all my sigmoidea are all cf. lutzi, but I will have to look at them all again before saying that. And I will definitely have to recheck my lutzi, rochai, and the queens of auropunctata.
On the subject of the queens, Jack has this to say:
"That “lutzi” queen is kind of intermediate between the type of lutzi and queens of auropunctata, so it will be interesting to see if you can sort queens into two piles, lutzi vs auropunctata. They may be really hard to tell apart. The queen you sent looks just like an auropunctata queen, just bigger than any I have seen. So they may just sort out by size, or there may not be any differences!"
So, that is what I will be doing next.