Comment by yobbo

For example, the size and fit of Seiko "calibers" are the same going back further than NH35, which means far older watches can accept NH35 as replacements. Even sub-assemblies and parts of NH35 fit straight onto 7s26s from the 90s.

NH35 can be serviced, but makes more sense an assembled replacement part. The same argument can probably made for the entire watch. The appeal of using one watch for 30 years is more in romantic fantasy than practicality.