Hello Leendert,
You're right, but I've just translated what I found - which is what is on
http://www.bhummel.dds.nl/gif/souburg.html. It could be that 'Eén groepscommandant verloor vier vliegtuigen' must not be translated as 'lost four planes', but as 'lost sight of four planes' - but well, I wasn't there.
The source doesn't tell what eventually happened to the 17 (or 18) planes, only implies that they were left in France eventually. What leads to another question: what really happened to these planes?
The webmaster of
Nederlandse luchtmacht in mei 1940 (Dutch Air Force, May 1940), of which the Souburg-page forms a part, names as source only: '
J. Molenaar, De luchtverdediging in de meidagen 1940, Den Haag, 1970, deel 2 p.1006 e.v. (bijlage 4)'.
Regards,
Bart