I have answered similar posts before...and what follows is only of course my opinion.
If you want to be totally 100% originality..then the watch needs to come from the original owner..who has never had it serviced, nor refinished..and ensure he gives you a signed statement of that. Or be truly NOS..and even then its possible parts have been replaced to bring the peice back to life.
Other than that you can get caught up in all manner of interpretations etc...like..is a classic car original beause someone has replaced the tyres for modern ones....sigh..
It can all then get rather silly I fear....with experts disputing certain things...bracelet type...dial colouration, box design..
So in summary
A truly original peice, by your definition at least would be a very hard thing to find and/or actually prove.
K