The collection of samples (the S&G and Thorowgood sanserifs together) suggests to me that images and data were taken from P.M. Handover's article "Grotesque Letters" (in Monotype News Letter 69, March 1963). There however, the "1825" reads "? ca 1825" ...
To date this Schelter & Giesecke sanserif, called "Schlanke Grotesk", back to 1825 is a mistake. Unfortunately, subsequent writer just copied this from Mrs Handhover. So much for writing history of type.
As you already noted, it is so perfect that it cannot be from such an early date. It can be found in part one of the "Muster-Sammlung", of 1886. But it should be hard to trace this back earlier for type specimens weren't dated back then.
(Side note: In the S&G specimen books you find other sanserif of much lower quality, more like the early British ones. These were -- I bet -- produced earlier than the fine "Schlanke Grotesk" which you showed, but later than the early British ones.)
Karsten












