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.
Monday.
Saturday
Saturday
It was a Wednesday.
It was a Saturday.
the day was Thursday
That day was a Thursday.
Thursday
15 February 1966 was a Tuesday.
5 March 1966 was a Saturday.
November 13 1966 was a Sunday.