Here's how I conceptualize the V4 lineage. It is based strictly on engine evolution (in the North American models) and has nothing to do with cosmetics, body styling, single vs dual headlights, etc etc etc. Minor engine characteristics such as cam profiles, valve sizes, are also too insignificant to matter.
1st Generation: began with 1982 V45 VF750 Sabre, Magna
Chain driven cams, forked rocker arms actuate a pair of valves each, shaft final drive, nearly vertical/horizontal cylinder orientation. Eventually included V65 VF1100 Sabre and Magna, and V30 VF500 Magna as well.
2nd Generation: began with 1983 V45 VF750 Interceptor
Chain final drive, engine turns opposite direction, cylinder orientation tipped back. Eventually included VF1000 Interceptor and VF500 Interceptor as well.
3rd Generation: began with VF1000R; mainly seen in 1986 VFR 750 Interceptor.
Gear driven cams. One rocker arm per valve.
4th Generation: began with the 1990 VFR750F
Gear driven cams. Direct valve actuation with shim under bucket. Single sided swing arm.
5th Generation: began with the 2002 VFR800-VTEC.
While the 4th generation was significantly revised in 1994 and 1998, the underlying motor stayed pretty much the same (though it got a slight displacement boost in 1998), so I don't consider those revisions to be a "generation". However, the 2002 model changed from gear-driven cams back to chain drive, and also gained the VTEC valve actuation system in which the engine operates on only two valves per cylinder up to 7,000 RPM, at which point an actuator engages the other two valves per cylinder. The point is to increase torque at lower RPMs. Breaking with long-standing 4-year tradition, Honda did not significantly revise the VFR for 2006 when it was due.
Further details such as 180 vs 360 degree crank can be added but this set of factors should be sufficient.
To complicate matters, the progression is not a single line. For example, the current Magna motors have shim under bucket valve actuation but use chain driven cams. They're an offshoot of the 4th generation motor.
Then there's the ST1100 motor, a longitudinal V4, which probably gets a category for itself.