FW190A-8 R2 "Black 10" of ii (Sturm)/JG300 Karl Spenst- Unknown Werknummer?

[Alte Hase]

Hi all...

Does anybody know the Werknummer of The FW190A-8 R2 'Black 10' of ii (Sturm)/JG300 flown by Karl Spenst? It was photographed at Lobnitz in November 44 doing a maintenance test flight, but no W.Nr is discernable...

Thanks!