Yavor,
Thank you for your reply. My source for the serial number is the online auction of a piece of wood claiming to be from this aircraft
Aviation; Baron Von Richthofen, Albatros Wood Laminate Piece, 3 inch. [p4a.com, ltd.]. Admittedly not exactly a thoroughly documented source. Windsock Datafile 79 has the Rumpler C.Ia (Han) batch from 4600 to 4799/16. 4508 and 4509/17 could be correct as I have an empty batch of 53 from 4503 to 4555/17 between three prototype Hannover CL.II and a batch of 22 LVG C.V. I could send you a copy of my updated file (later than that on my website) for your perusal if you like. Thank you.
Roger