Florian
You mention the French 1966 "Pour le MUSÉE POSTAL" souvenir sheet
as an example of TD -6 composed of 1 plate
direct plate printing / line engraved recess printing = taille-douce 3 couleurs
and 1 plate
indirect plate printing / offset-recess = taille-douce report 3 couleurs
I believe I have the stamp France Michel 1552 somewhere but
have never seen the special Souvenir Sheet.
The old Michel I have states that the stamp was printed combination
StTdr und RaTdr (Steel recess and
photogravure)
I have to admit I had never heard of
offset-recess before it was mentioned here
by Rein.
Just shows there is always something new to learn about stamp printing. New to me at least.
I'm always surprised at the lack of interest shown
by most stamp collectors when it comes to stamp production.
For instance on this forum out of lets say a couple hundred members
who are regular posters there are maybe half a dozen really into this stuff.
But what the heck , to each his own.