Odd 50s/60s size label

[plousia]

I have this 50s or 60s Highland Queen skirt that has a "12" size label. But the waist measures 30-31", not like any 12 of the era I've ever seen. Does anyone know what size system they might have been using, or seen this type of sizing before?

I am sure of its age because it has the union label used between 57-68, construction is right, and it doesn't have a Woolmark label.

 

[The Vintage Vendeuse]

It looks like a wrap style? Maybe the original owner moved the closures/buttons to accommodate an increasing waistline?

 

[plousia]

Oh my YES. We have a winner! Definite evidence of the buttons being moved. Thank you! There are some smart people on this forum.