I think there was also a problem with the 7,000 year creative days in general: This used to be said to imply that all animal and plant life was less than 40,000 years old - clearly an absurdity.
Nowadays, they hint that the creative days could have been "thousands" of years long, apparantly.
But, without the signifigance of the 7000 year day, 1975 just doesn't mean squat. No matter if 607bce is right or not.