[Pieter H]

Larry,

It seems that KG4 was making a bit of a mix-up in May 40.
On the one hand some Staffeln had suffered losses in Norway, while at the same time III. Gruppe was replacing its He111's by Ju88's.
Apparently they have been shifting around aircraft to fill holes, sometimes with and sometimes without their crew.
For me the most convincing argument is that III./KG4 (both He111's and Ju88's) attacked airfields in the north-western part of Holland: Schiphol, Bergen, Soesterberg. Several losses around these fields confirm this, see Peter Cornwells lists. I can hardly imagine these crews, after having been received by substantial anti-aircraft defense and interception by D-21's and T-5's, simply continued south into the even bigger chaos over Rotterdam Waalhaven.
All reports consistently say Waalhaven being attacked by I./KG4 and 5./KG4. Also there is the report of the two G-1's of Buwalda and probably van der Jagt shooting down two He111's out of a Rotte that crashed almost simulataneously. These are the two listed in your mail.
So yes the aircraft had codes of 9./KG4 and apparently the crew of the 5J+ST was still formally belonging to 9. Staffel, but nevertheless it seems they operated under the command of 2./KG4. The question then becomes which fact you give the higher weight for labeling them; either 2. or 9.

By the way, other sources (Brongers) give the a/c code of the first one as 5J+BT.

Regards, Pieter