The open o was on the first Greco Mint Collection series around 1981/1982 and the open o stops around 1990.
At the same time Greco also made some Grecos with closed o's and also made some closed o's in the early 1990's.
So I would say a Mint Collection has a open o but other people might say that the closed o's from the early 1990's are also Mint Collections it's hard to say exactly as Kanda Shokai who made the Grecos did unexpected things sometimes.
The set neck Grecos up till 1982 can have a 70's Gibson tenon which is not the long tenon everyone knows.
It's a tenon that stops at the beginning of the neck pickup hole or fingerboard end rather than extending into the neck pickup hole like a long tenon.
The Mint Collection series mostly do have the 50's Gibson long tenon.
Personally it makes no difference to me both tenon types are better than the modern Gibson tenons which are very short.
There are a fair few Mint Collection models.
Here are a few and their original selling price in Yen.
As the prices go down the pickups also go down with the Dry pickups reserved for the top of the line.
EG58-120 DRY 120,000 Yen
EG-59-70 DOUBLE TRICK 70,000 Yen
EG-56-60 HOT LICK 60,000 Yen
EG-59-50 SCREAMIN 50,000 Yen
EG59-45 SCREAMIN 45,000 Yen