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.
I've just come across something on google search regarding the word 'Julien'. I don't know if you or the Etling project already know this ... you probably do...
Under a 'book' called Ceramique et verrerie 1937 only a 'snippet' of info to see but it appears that on page 68 there is a mention of a M. Dreyfus (not Dreyfuss with 2 x s at the end as mentioned in the Brief History page on the Etling Project site) with in brackets after his name is written '(Julien), Societe Anonyme ETLING EDMOND), Bronzes et objets d'art, 29, Rue de Paradis, Paris 10th.
Source here:
https://www.google.co.uk/books/edition/C%C3%A9ramique_et_verrerie/Pg2ld7_8KdUC?hl=en&gbpv=1&bsq=edmond+etling+choisy+le+roi&dq=edmond+etling+choisy+le+roi&printsec=frontcoverAnd another mention in another book that Julien Dreyfus was Etling's nephew?
Could it be a link to glass marked Julien?
I'm just adding a link to a much older thread here on the GMB but I guess info and knowledge has moved on since then!
https://www.glassmessages.com/index.php/topic,11976.msg84601.html#msg84601