Mystery ships and the Admiralty of Amsterdam in 1652 and 1653

Especially with respect to ships built as warships by the Admiralty of Amsterdam, I don't believe in "Mystery Ships". Abraham van der Hulst seemed like a compelling case for the existence of a "Mystery Ship" (one that we did not know about from published sources). The problem with the concept of "Mystery Ships" is that the ships in service with the Admiralty of Amsterdam in 1652 and early 1653 were very well-defined. The relevant documents are the following:

The Board of Admiralty in Amsterdam to the States General, dated 5 August 1652
  This is a summary of the ships in service and their employment, 
  although only captains are mentioned (published in The First Dutch War, Vol.I)

List of ships under the control of the Admiralty Board of Amsterdam
  This is undated by from the contents, appears to be from about mid-March 1653
     (published in The First Dutch War, Vol.IV)

Staat der Nederlandsche Zeemagt, in Maart des jaars 1653
   This is an outline of the strength of the Dutch navy, organized by 
     admiralty, and not listing ship names or captains, but is a 
     summary list. Many ships can be identified from the outline and
     the sailors and soldiers in the crew are specified for the 
     Admiralty of the Maze and the Admiralty of Amsterdam
      (published as Appendix XXII to Vol.I of Geschiedenis van het
        het Nederlandsche Zeewezen)