Thanks -- yes, I've already seen that page and the similarity to the Reich pattern.
Regarding the comment: 'It makes it guess that Costebelle was an Artist (artistic name) who worked for Etling Project, like Georges Béal', I had considered this, but I think those designer marks are usually (always?) seen in addition to the Etling mark. In the case of these lidded pots, the examples I've seen have either been marked Etling or Costebelle and have never carried both marks. That said, I seem to recall the Loetz production for Etling was simply signed 'Richard' and didn't mention Etling either.
Other possibilities I'm considering are that may be Etling didn't have exclusive rights to some of these more common patterns, meaning that other retailers could sell them under their own names, or maybe the designs were issued under different names after Etling's store closed?
Certainly there are other instances of documented Etling designs seen with other marks, most famously perhaps 'Julien', but there's also an Etling wine coaster which is sometimes seen with 'Cesari' marks.