Maybe I am wrong and my take is too simplistic/naive (as I admit, I haven't thought too much about this topic), but imo aggregating publicly available data shouldn't count as stalking. Acting on that data in a way that could be constituted as "stalking" definitely is real stalking though and should count as a crime.
For example, if someone's ex (who was explicitly warned that he was unwelcome) continues showing up at the doorsteps because they remembered your address from a long time ago, then it is stalking. Them knowing the address isn't.
In light of this, I don't see how it matters whether they remembered the address from past experiences or just found it through a website that aggregates publicly available info. As long as the data was obtained legally and without breaking any other harassment clauses, why would just the knowledge of something be a crime?
I see it just like firearms. Having a firearm (in a lot of US jurisdictions) is not a crime, as long as it was obtained legally. Doing harmful actions with it (such as threatening people or shooting someone who didn't pose a threat to your life) is a crime. Having a firearm feels like just having data, in this scenario. As long as you don't use that data for criminal actions, why would just the potential of you being able to do something criminal with that data is a crime?