The WaA251 is identical between the two pistols in terms of appearance. It is in different locations. On the Mab-D on the frame above the trigger guard and on the spur (again on the frame) of the Star B. According to the
http://claus.espeholt.dk/mediearkiv/WAAE.pdf site, this is the correct WaA for French and Spanish items included the Unique, Mab-D, 1935A, 98/G41/43 parts, Astra 300, and Star B. If it was faked, why would they go to the trouble of researching the correct stamp to use and not place it in a similar place as on the Mab-D? Why put it on the spur? No other pistol to my knowledge is marked in that area?
Also, authors have been wrong before on serial number ranges. I believe I remember hearing that all the records for the Eibar plant for this pistol were destroyed or are missing.