Well, I figured out what went wrong with Camilla. It is incredibly stupid. The instructions for the yoke decreases read: *K1, k2tog, work to 2 stitches before marker, ssk, slide marker; repeat from * 3 times – 8 stitches decreased. Here is where I should have checked my stitch count to make sure I was actually decreasing by the correct number of stitches each row. Because I got confused and only did the decreases inside the sleeve markers, not on each side of each marker. Here is a drawing to illustrate my error:

The little rectangles represent stitch markers. The decreases in red are the ones I failed to do. I was only decreasing 4 stitches per row - no wonder the neck is twice as big as it should be. (HUGE SIGH) Of course, I also neglected to do a gauge swatch, so the whole sweater turned out bigger than I intended. Eventually I’m going to rework the yoke and try to shrink it a bit. Right now it’s balled up in a box of Christmas decorations because looking at it made me angry. And then embarrassed of my mistake.
I totally understand. I have a beautiful whisper cardigan that is at least 2 sizes too big. Who knew, you should always swatch, even when you don’t want to. Dur.
Omg. I am so glad I found this post. I’d already frogged the baby version once before realizing that I was neglecting to do the same decreases! So glad you did this post otherwise I’d be pulling my hair out.
Let me second what Christine said – I am working on the baby version and put it away because I could figure out how to both follow the directions AND make 8 decreases per round. (This perhaps suggests that the pattern directions may not be as clearly written as they might be?) Your post may well save my sanity – and my sweater.