In the 1922 Bottin this firm had just a 2-line entry, presumably the merger had recently occurred, but by 1925 it had a full display listing five marques:

Papeteries de Levallois-Clichy et Atelier d'Art réunis

(From ANNUAIRE DU COMMERCE DIDOT=BOTTIN 1925 Paris:)
Impression photographique en tous genres. Cartes postales bromure.
Editions:
  PC - grand luxe
  RP - grand luxe
  REX - de luxe
  FURIA
  JK
Bureaux et administration r. Beaurepaire, 30 Paris.

Before the merger, in 1922 the marques RP and FURIA had belonged to L'Atelier d'Art, under which they are shown on this site. In 1914 the marque JK had belonged to J, Klepetar, under which it is shown on this web site. REX cards were also produced earlier, in WW1, publisher unknown by me. Card 768 on the next page is an example.

There are also some modern-looking glossy cards with REX and PC logos, more antique-looking pictures (eg multi-baby) and numbers which conflict with earlier cards.

from ANNUAIRE DU COMMERCE DIDOT=BOTTIN 1925 Paris

Next page, example cards