Vintage has (since few years ago) been difficult to grade, ie; pop control. Personally I witnessed it myself (a few different occasions) when I sent in a mint copy of vintage card to PSA and got an 7 or 8 back. But when the same card was broken slab and resub to BGS, it got 9 or 9.5 back!
Since then, I totally gave up buying raw vintage cards, sending in for grading. I simply just buy graded slabs.