Several points here:
1. Patents only last for a finite period of time. Usually 18 years.
2. The film and coupler patents are out there, and most have expired. The entire Portra structure is out there.
3. It takes a trained engineering team to understand and reconstruct a film from a patent. You also need a lot of equipment to do it.
4. Patents don't tell everything. Many tiny bits are left out, and these bits are critical and in the mind of the current engineers at Kodak. There are only about 200 of us left living. When we are gone, those little bits are gone as well.