We know the Tangent Piano alongside their names because they made and developed this type of piano to its perfection and inspired other makers and musicians by their great craftsmanship.
We know at least one of their Craftsmen through Gerbers Lexikon : Johann Ludwig Berner.
We do not know of any other makes being their pupil or craftsman like Berner but since Spath & Schmahl's tangent pianos were so wide-spread all around Europe, many piano or organ makers nearly copied or made very similar instruments which clearly shows they had a Spath & Schmahl tangent piano in front of them! like Silbermann who must have had a Cristofori piano at his workshop because the action he made for his pianos is absolutely the same as Cristofori with one small difference that the Cristofori's travelling hammer distance (from the resting hammer head to the string) 2cm but those of Silbermann being 4cm.
The same story is about several other makers who almost copied a Schmahl one. One can see that they surely had a Schmahl tangent piano there because most details are exactly like Schmahl's while
they could look simply different if they had their own design.
The previous models of tangent pianos (like those designed by Pastore and a few other German builders)
Franz Jakob Spath was born in Regensburg (1714-1786) son of Johann Jakob Spath (1672–1760) himself being a notable organ maker. He must have learnt his craftsmanship from his father. He received ''das Patent des Orgel- und Instrumentenbauers'' in 1747 and continued his father's workshop after his death in 1760.
On 6th of Oktober in 1747 he married Johanna Rosina Spath (ca. 1720–1790) with whom he had only two daughters. Christoph Friedrich Schmahl (1739–1814) being Spath's pupil married his daughter Anna Felicitas.