Beautifully said Jens!!!
I agree completely with what you and Radu have well explained here. The cartouches were often added at a later time, and typically were prayer invocations. In later times as commercialism increased and the use of trade blades intensified it was indeed very common for makers to add the names of earlier and more renowned makers to enhance the value of the blades.
For probably one of the best resources that addresses cartouches and markings found on many shamshir blades, I would very highly recommend
"The Persian Shamshir and the Signature of Assad Allah" by Oliver Pinchot ("Arms Collecting" , Vol.40, #1, Feb.2002). The author is well known among serious collectors and students of Islamic arms and armour, and goes into considerable well explained detail describing the development the shamshir's favor and the later advent of production blades that occur frequently on many examples. His attention to the cartouches, as discussed here ,is of course key to his article.
The beauty of the Persian shamshir is always astounding, regardless of the age of the blade, and those who own true examples are very fortunate indeed!
Best regards,
Jim