I can give a bit of insight into Rover Model identification. It has remained largely consistent.
The first two numbers were the chassis model. The last digits always designated the engine. A number or numbers were inserted between these two groups when changes were made to the original design series.
Example. The great 3210 first appeared in the 1960s. This was a Model 32. chassis coupled to a 10 Series 4hp Briggs.
Later a 13 series [5hp]engine was added: this was the 3213.
By the late 1970s the chassis was redesigned with a high arch. A number [1] was added in-between the two groups.
Thus the new designation for the 5 hp became the 32113. When the 13 series gained industrial/commercials the engine number had to be changed. Thus we had the 32123.
Under successive owners, Rover seem to have somewhat retained the original Rover Mowers model identifiers. First numbers deal with chassis and changes to it. Last numbers are allocated to the mated engine used.
The last numbers are now arbitrary [factory allocated]. They may designate ancillary changes [starting], hp changes, or engine make changes.
