I agree Clint
The problem with these early photos (well almost everything sold on e-bay) are we simply lack both dates
and places, so all we can do is to make a "best guess".
I usually myself date photos like this as "pre-delivery" since I don't think the German Army flew around
for long with aircraft lacking national markings at least not post 1913.
The further on we get in time (1914 and on), I believe the manufacturers painted up these Army markings
directly before delivery, including the Bestellnummer.
The problem with these early photos are we lack not only dates/places but also much other data.
For instance I have no idea where WNr 151 was going. To the Army or Aviatik's own school?
Since I am in New Zealand right now I cannot check any books or other data from back home....
Cheers
Stig