Eric, many thanks for the links! Managed to translate the relevant part of the first. It would seem to confirm that some unmarked graves in the cemetery at Bergen op Zoom are probably the remaining missing crew from HK602. One of these graves is an unidentified Flying Officer.

Unfortunately, haven’t been able to do much with the second link?

From the first link:-
Lancaster Mk.I HK602 of 90 squadron – started at 0818 from Tuddenham Suffolk with the aim of the batteries at Vlissingen – collapsed at 1002 due to Flaktreffers in the Westerschelde.
With the exception of a single crew member, the entire crew has been missing. According to the report of the airguard of the shipyard “De Schelde”, four parachutes ended up in the sea just outside the Buitenhaven. However, the Bomber Command Losses report two drownings at sea and two paratroopers, who ended up in the explosions of the discharged bombloads and of which (obviously) nothing could be found anymore.
In the months that followed, the remains of various British airmen washed ashore near Ritthem, after which they were temporarily taken to the sea dike.
ordered. None of these bodies could be identified, but it can not yet be ruled out that one or more of them belonged to this crew. Flg.Off.Robert Josephus Constable Higgins mia
Runnymede Memorial Panel 206
Sgt. David Alexander Robertson Walker mia Runnymede Memorial Panel 239
Flt.Sgt. Lawrence Gordon Calman RNZAF mia Runnymede Memorial Panel 263
Flt.Sgt. Francis Frederick Austerberry RAAF +
His remains were transferred at a later stage to the military cemetery in Bergen op Zoom.
Flt.Sgt. Bernard Coward mia
Runnymede Memorial Panel 216
Flt.Sgt. Donald George Headland mia