I came across this wine for $20 as a one off at a reputable online retailer, and picked it up to fill out a case. I know next to nothing about what to expect from the bottle, so am asking for thoughts on how it might show, history of the producer, etc.
And thanks for the link to the old article - it was a fun read. Many old stalwards in the list and in addition to the Dao I suspect the ' 78 Spanna might also be drinking well
Tcwc.com has fun stuff pop up in their Portuguese section pretty regularly. Their pricing can be all over the place though, sometimes nice deals, other times you just scratch your head.
I had a unknown vintage 1970's Dao white from Constantino a year or so ago that was good for about 45 minutes or so, then started a decline. Amazing it held up that well. So here's to keeping fingers crossed.
Grão Vasco brand is owned by Sogrape (Portuga's largest producer) and I believe Sogrape owned the brand in 1977. Today the Grão Vasco brand is a bargin brand selling for a couple euros a bottle here in Portugal. Certainly not a wine that you would look to for any type of typicity/excellence from the Dão.
That said, I have no idea what you should expect from that wine. I recently opened a magnum of a 1970 Dão wine that I found in my in-laws house and it was good/interesting. Wine making in Portugal was quite dodgy in many regions for many many years (really until joining the EU) so who really knows what went into these old bottles.
Enjoy the wine, report back.