Explorer 39mm and random serial number anomaly

[SPG8]

Given the Explorer 1 39mm was released in 2010 and that seems to be the first year of random serial numbers, why have I recently seen brand new 39mm Explorers in authorised Rolex retail outlets with "G" serial numbers as well as rather long mixed alpha/numeric serial numbers?

In one case the dealer's inventory showed a G watch was delivered by Rolex 2 weeks prior!

Could it be that random numbers lead to such an anomaly? Or, could Rolex have simply used a production process whereby cases were ready for watch assembly and thus serial numbers take time to move through the system? But 2 years is a long time!

I suppose in some years time in the used watch market the resale of 2010+ Rolex watches will rely less on actual year of manufacture for pricing and more on simple condition etc..

Any views?