The development stages of the Tempo microcar project were:
1) An angular scale model with 3 wheels (single rear wheel) and four doors
2) A well-designed scale model with four wheels (narrow gauge rear axle) and four doors
3) A scale model with four wheels (narrow gauge rear axle), just slightly altered design, but now with two doors:
https://www.autopuzzles.com/forum/2011-39/solved-allemano's-8470-628-1955-scale-model-microcar-project-vidal-sohn/4) A real car (Kleinwagen Ausführung A according to Schumann's book) of the same design, powered by a Heinkel two-cylinder engine from the Hanseat. It was built in 1955. Initially of white color it must have been repainted in a two-tone colour scheme later and fitted with a license plate issued 1957 or later.
5) A real car (Kleinwagen Ausführung B according to Schumann's book) with a full width rear axle which is this puzzle car.
6) A 1957 scale model of a larger car planned in cooperation with Hanomag, to be powered by the Wiking's Heinkel engine or the Matador's Austin engine:
https://www.autopuzzles.com/forum/2009-37/solved-291-of-all-1957-vidal-sohn-(tempo)-project-y/The last one is known as Projekt Y, so my guess would be that someone drew the conclusion that the former car must have been the X. In Pfannmüller's Tempo book he calls #5 the X, but is also wrong in naming #4 the Y, probably confused by the more modern number plate of the two-tone car, and naming #6 the Z. He states that "the Y" was later given to Nawalmal Kumar Firodia, the Indian Tempo partner, as a present. This might be the reason for the update in appearance of #4.
