NSK, rod222 and lithoengraving,
Thank you all for such wonderful information, well beyond my hopes. I was working from the Michel catalogue "Deutschland 2016/2017" and the information is not listed, nor it is listed in my more detailed Michel catalogue "Deutschland-Spezial 2016". Lithoengraving, was the catalogue you illustrate the Michel 1991/92 specialised, band 2? If so I must get a copy because it looks like I am missing out. I also didn't think to check the similar entry for the Bundesrepublik but when I did, still no luck in my more recent editions.
I offer the following as a timeline.
The Melton Prior institute website has that superb interview with Rudolf Riess in which he says that a wood engraving of Herr Bundespräsident was done by Willi Seidl in Stuttgart, direct from the photograph by Liselotte Strelow. The website captions the engraving with 1959 but considering the 10pf and 20pf values were issued on 31 January 1959 I would think he did his work in 1958. Of course the 10pf and 20pf values were typographed but they were surely designed direct from the work of Willi Seidl, not from the photograph.
The picture of the work of Willi Seidl shows it as a wood engraving (done on the endgrain of the wood, specially prepared) rather than a woodcut, which is done across the grain of the wood with different tools.
Working from the portrait by Willi Seidl, M.E. Cordier then designs all five stamps and the Bundesdruckerei decide to do the lower three values, to be issued first, by typography and the two top values will be printed intaglio. Egon Falz then engraves, in recess, the dies for the 40pf and 70pf values.
I must say that seeing the original wood engraving I do like it a lot, moreso than than the smaller version on the stamp. I have included below a detail from the 10pf typographed and the 40pf engraved just to compare. Whatever techniques were used to transfer the design from the wood engraving to the typographed stamp it does not produce as nice a result as Egon Falz did by hand.