Here is a special bark-like pattern 75 made for Boucheron, which look to be completely different from the the Parker production Écorce.
The material is also different as this Boucheron pen is made of sterling silver as seen by the "925" hallmark indicating it is made from 92.5% silver. The Parker production Écorce is gold- or silverplated brass.
This pen was depicted on page 145 in the French book "Un Amour de Stylo" by Robert Laffont, The description accompanying a photo of this pen was "Parure Parker. Boucheron, argent et or motif écorce" which translates to "Ornamental Parker. Boucheron silver and gold bark motif".
This pen was also shown in a French 1991 auction catalog.
The item description was "Exceptionnelle parure de stylos en or blanc massif décor écorce." which loosely translates to "Exceptional ornamental pen designed in solid white gold with bark decoration".
We know from the above close-up picture this pen is definitely not made of white gold, which in France would have been required by law to be solid 18K.
In conclusion I believe that the use of the word "écorce" in the book and auction catalog was only descriptive. After all it is the French word for "bark" and clearly the pattern does appear bark-like. I do not think that this was the actual model designation used by Parker even if it was private-labeled by Boucheron.