Florian nice to see you back posting again.
Here is a detail from the souvenir sheet you asked for...
and here the sheet stamp and the SS stamp side beside
There are differences especially in the light colours.
Look at the red lines in the cap of the postillion.
The sheet stamp lines are approx 125° whereas in the SS stamp
the lines run approx 30°.
Even the black direct has differences such as the
letters on the mail satchels.
Sheet stamp a T
, SS stamp an R.
So going by what you mentioned previously the 3 indirect recess colours (orange,red & blue) where printed on one pass and
the direct recess black on the second.
I wonder if Slania engraved only the one colour direct recess
and other engravers did the colours?