Since one portion of the date, whether it be the month or the day, is unspecified, it is impossible to know which date you are referring to.
February 12, 1966 fell on a Saturday.
It was a Wednesday.
Monday.
Saturday
Saturday
the day was Thursday
It was a Saturday.
That day was a Thursday.
Thursday
December 17, 1966 was a Saturday.
May 10 1966 was a Tuesday.
September 20th 1966 was a Tuesday.