Is There a Difference Between Service Replacement and NOS

[BristolCavendish]

Curious. For those seeking to improve the cosmetic appearance of an older watch, there seems to be a distinct differentiation between original, service replacement and an upgrade via sourced NOS components.

While many can detect 'service replacements' is there a major difference between an original vs NOS component other than one is newer and free of age-related flaws?

It seems that most vintage aficionados prefer original but there will be times when older or dilapidated parts equate to crappy-looking (at least from a visual reference point).