As far as flat-twin Kocos are concerned :
- one source only mentions the 4/16 PS model, without pictures
- another source mentions both 4/16 PS and 5/25 PS models, without pictures
- a 1922 4/12 PS HK1 model is featured on lots of websites, with pictures; it's similar but not identical to the puzzle car
- the actual puzzle photo is featured on Koco's website with a "Carl Koch 1919" or a "pionier-carl-koch-1919" label but without any model name
Therefore I would argue that the puzzle car is an early 4/12 PS HK1