Vintage or not, you measure from the row of the marker, not along the edge.
However, just because the pattern says that 9 inches is the correct measurement, it doesn't necessarily make it the right size for you. Find a sweater or shirt that you like the fit of and measure that. Then make your sweater more personal if need be.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry