Not really common practice. Old parts were just boxed up and used for parts dept inventories.
Old parts being used on early pilot cars pre-production cars is because the new parts weren’t ready yet. Those small number of cars end up in brocheres, magazine tests, and parts catalogs.
Some parts carried over for a while. But the parts interchanged with: form, fit and function. The front mounted locks don’t function the same. They don’t offer the same safety and convenience
The 69 doors take different lock linkages parts too.