Phoebus 1

Ok, this is what I call V2,5. I have found it on early 1920s bun feet Phoebus models 1 and 30.

V3:

V2,5:


Nicola

 

And we can also connect the Mickey Mouse filler cap to early 1920 and logo v2,5:



Nicola

 

Nicola: sometimes the catalogues are only approximate in the images they print - often older images make it into later catalogues, sometimes rather illogically. I'd say that your observation is pretty correct: flat cap to around mid teens, then Mickey Mouse, then the more familiar later one. Similar for other makes also. They seem to have all kept an eye on what each other was doing.