Vandersteen makes running changes to models without changing the name (other manufacturers also do this, eg, Ayre). The 2Ce Sig II got a new midrange driver circa 2012 that was unannounced and I think RV made one or two other changes before the Sig III. So, the change from "Sig II" to "Sig III" is more than the crossover and removal of tone controls. I also know from experience that upgrading the crossover can make a very substantial difference so I'm not going to poo-poo that change.
Also, I'm confident a 2020 3A Sig is not the same as a 1999 3a Sig.
Also, I'm confident a 2020 3A Sig is not the same as a 1999 3a Sig.