"Van Poelenburgh", "Van Cuylenborch", what's the difference?

Galerie Moderne, from Belgium, sells on 16 October 2018 an "attributed to Cornelis van Poelenburgh" Antique ruins with Diana, on oil on panel estimated at 3,000 to 5,000 Euro.

The attribution to Van Poelenburgh (1594-1667) is understandable, he is known for similar nudes in landscapes, but they are usually situated in the open, with rather different colouring. These cave or grotto scenes in brown are much more typical of the work of Abraham van Cuylenborch (1620-1658), and this fits nicely in with his known works.

The above  "Nymphs in a grotto" from the Statens Museum for Kunst in Copenhagen has the exact same left side of the painting, and seems to be comparable in quality (but the image is too small to be certain).

The work for sale is actually very well executed, and is at least a good workshop version.

A lot of paintings attributed to Cuylenborch (but of varying quality) appear at auction though, and many remain unsold, so the market for his work is not very strong at the moment. Despite the real quality here, and the direct link to a museum piece to strengthen the attribution, it may struggle to get much more than the estimate. Which is a shame really, as it should be worth 10,000 Euro.