The symptoms of vortex ring state can be encountered any time the downwash velocity equals or is very close to the rate of descent.
As the downwash velocity will vary along the span of the rotor blade, the symptoms can be encountered in more conditions than just the absolute classical case.
When entering using the method I described (much) earlier, the downwash velocity is initially pretty low, because you're at a reduced power setting. As you start to descend (due to power used being less than power required to maintain a hover), you may be in a (dare I introduce a term here) partial vortex ring state - that's what makes the demonstration not totally repeatable. If, as you start to descend, you were able to match the average downwash velocity from the rotor, you'd have the classical 'total' vortex ring state.
I've never been lucky (?) enough to get that to happen in all the demonstrations I've done, but the symptoms that show up are sufficiently convincing that all the pilots I've done this with have said they've come away with a better understanding of the scenario.
To recap - anytime the downwash velocity equals the rate of descent you should encounter (some of) the symptoms of vortex ring state. Learn those and either avoid the situation if possible, or know when and how to get out it.