Monon Lettering

[Steve Ford]

I've noticed there are mainly three types of lettering used by the Monon (CI&L) on their steam engines.  A block serif typeface, a traditional serif typeface, and a block san serif typeface.  Does anyone know when each typeface came into usage?  I assume there would be some overlap between styles, but just general dates would be fine.  I've attached a picture to give a better representation of them.

Thanks,

Steve Ford