Edwin: In a recent publication, it is confirmed that Lange did produce 5 pieces of the black dial version in 2004. They were made to commenmorate Sincere Watch's 50th anniversary of its founding. The serial number 1/5 piece was auctioned for nearly Singapore $ 200,000. In 2005, one of the 5s was sold by auction house Sotheby's for HK $ 960,000.
In 2006, as you rightly pointed out, Sincere offered, as part of the World Exclusive Collection, 10 pieces of the RG/Black dial Double Split Limited edition.
Best regards,
Sam