I was going to add this observation onto my previous post about the evidence of pleated shifts found at Birka, but figured that if I did so, no one was likely to see it or comment upon it.
Shelagh Lewins's reconstructed apron dress based on the Køstrup find has given me another thought about the pleats found in the Birka brooches. Her dress uses loops in the back that are as short as the loops in the front. One practical consequence of this design feature is that the dress rises very high in back and is unlikely ever to shift significantly in wear. Another consequence of this feature, however is that her brooches rest very high on her chest--even closer to the neckline of her shift than mine are, as this photograph of her shows, and well within the area of the deepest and densest pleats on a full shift pleated into a close-fitting neckband.
I don't think all apron dresses were made this way, since it seems unlikely that an apron dress made in that manner would be unlikely to turn upside down on the body, as Bau noted some of the brooches found at Birka appear to have done. But some of them might well have used short loops and been worn just as Shelagh suggests.