I know that if there is no information in 'Metadata' the date field is filled with the current date & time. However, if I have a photo where I only know the year it was taken and enter JUST the year eg. 1982 the date is saved as 1982-07-10. The field will add the CURRENT month and day.
Is it possible to stop the date field from doing this?

If I enter just Year and Month eg. 1982-07 then the date is saved with the day set at 01. (1982-07-01)
If i enter the date as 1982-07-00 the date is saved as 1982-06-30. These last points are not of major concern because if I know the year and month then entering an arbitrary day eg. 1982-07-01 will retain the year and month.

The database field (if you are referring to that) requires a valid date format. And that format is simply y-m-d so any missing part is added to be valid.

1982-07-00 in any case is not a valid date so no wonder it takes the next correct date instead.

There is no way around this, you have to enter either a valid date or leave it blank so the current date is used as you noticed.