I think there are a couple of points here:
- We are always comparing to human consciousness and we don't understand consciousness in humans well enough.
- You can always retain some form of solipsism and be sceptical of any consciousness outside of your own.
But with these things in mind, there are vast differences in the ways AI systems can exhibit consciousness (whether that's real or not).
The key question isn't "do we understand it?" but can we disprove it?
As an example, what a "country" is is well understood but not well defined. There are all sorts of examples of places that either are or are not a country depending on whose definition you use - transnistria, Nauru, Vatican, Somaliland, etc.
You could argue that passing the Turing test equates to consciousness for instance, which is fairly well defined. In which case it was achieved in 2014 (I think?).
Or not - but if it's not, what is the definition?