Yes, it used to be common...although less so today. Basically, if you want to be an Authorised Dealer, you have to commit to buying certain volumes from the manufacturer. If a Dealer feels that the commitment he needs to make is more than he can actually sell, he may make the commitment anyway to keep the franchise. He will then sell the "excess" watches to a grey dealer.

Doing this is a breach of the Dealers agreement with the brand, and of course the brand can tell which serial numbers it sold to each Authorised Dealer and whether these are now on sale from a Grey Dealer. This is why the serial number is removed- so it can't be traced back to the Authorised Dealer.

The downside for consumers is that many ADs will refuse to service a watch with no serial number..that's why Grey dealers offer their own warranty.

So, in summary, they are original watches that have been sold through (legal) back channels, but they have lower resale value than "official" watches because some buyers insist on having the serial numbers and there is potentially difficulty in servicing.

Its now less common to see serials removed on Grey watches- not sure why

dc