Many watch buyers come in with different ideas of what makes a watch "authentic", and that's fine. Some may think it means that the watch must come with all the parts it came with from the factory, some believe in other less strict definitions. However, there is a generally accepted standard for what makes Omega watches "authentic". 

Generally Accepted Definition:
The generally accepted definition for an authentic Omega watch is the following:

- The movement is an Omega movement
- The case is an Omega case
- The serial number of the Omega case matches the serial number of the Omega movement
- The watch must be serviced with parts appropriate to it's model 

By this generally accepted definition, the following are considered "authentic""
- Omega watches with no parts replaced or serviced
- Omega watches serviced by Omega with Omega parts (note that Omega may service an older watch with a newer part that may not have come with a watch of that vintage (for example, watch dials with older tritium lume are no longer produced)
- Omega watches that have been serviced by a third party with Omega parts appropriate to it's model
- Omega watches that have been serviced with aftermarket parts appropriate to it's model

The following are not considered authentic.
- Omega watches that have a movement that does not belong to the case (serial numbers will not match)
- Omega watches with parts replaced to make it look like another Omega watch (often done to make the watch look like a more valuable model)
- Watches that have an Omega movement, on a non-Omega case
- Watches with an Omega case, and a non-Omega movement

Vintage Watches
Some watches will be sold with qualifiers such as "all original parts", these are usually only relevant to Omegas of 1960's vintage or earlier, where the presence of all original parts makes them significantly more valuable than one with replacement parts (even Omega replacement parts!). For watches of modern vintage, replacement parts generally do not affect value.

Boxes and Papers
For limited numbered edition Omega watches, boxes and papers may help determine if a watch is authentic, especially if the paperwork is numbered along with the watch.

Generally speaking though, boxes and papers (including warranty cards) can be purchased separately and assembled together to form a set (Watch Vault NYC does not engage in this practice). Original boxes and papers can be pared with any fake watch so they should not in be used as the sole method to determine authenticity.