The other way of considering the difference between VRS and SWP is to look at Nr.
In SWP, you have run out of power - but keep pulling anyway - the Nr will decay and you will descend - often to ground impact.
In VRS, you have run out of lift - because of the stalled roots and the vortex-ingesting tips - you can get to this stage without running out of power.
The 'lesson' given to students about VRS often involves flying downwind at 1500' or so, reducing speed below 30 kts and then allowing a slight RoD to develop - at this point the lever is raised and the ensuing vibration is described as VRS (it isn't VRS) and immediate recovery is made by increasing speed and flying out.
The student is scared by the vibration and the instructor has shown the conditions for entry - everyone goes away happy but there has been no VRS demonstrated or recovered from - only what we are now calling IVRS.
It's a bit like the difference between FW spin recovery (from a fully developed spin) and incipient spin recovery - one involves a specific series of actions to recover from the high RoD into controlled flight and the other usually just requires centralisation of the controls.
The difference between incipient spin and fully developed spin is large - in exactly the same way that the difference between IVRS and VRS is large.