I haven't come across this with the 200's but I am able to conform that the Chott never did have an engine number,
what has happened in the past, is that the 42 officially UK imported Chotts (Slater's) had the chassis number duplicated so as to "create" an engine number,
This is what I have done for dating certificates for imported at a later date Chotts and 2TR's, I am not even sure if this is legal, but it is what I have done, .The thing to remember here is that the chassis number is all important, because it is properly referred to as the "VIN" (vehicle identity number) and that is what the registration paperwork and registration plate identify, the engine can be changed multiple times willy nilly without affecting the VIN, it is also possible to get a registration paper with the numbers expressed as "illegible" (in the case of the engine, don't know about VIN) as might be the case with a 1902 Packard I imagine that is where the flexibility is coming from.
CLEM