A business needs a registered address, but it doesn't need to be the address of their main offices. It's quite common to have a registered address which is just a forwarding agency.
I guess you could mail a cellphone or AirTag to their registered address, then even if they find it and don’t forward it, you could follow the person(s) who fetch or deliver the mail to the company location.
You could maybe even skip the mailing step and just watch the registered address and trace the movements of everyone who visits that location.
Watching the location is a bad idea. I’d hazard a guess that most forwarding agencies have more than 1 customer, so you’ll be on a bunch of wild goose chases.
Also forwarding agencies probably don’t visit the clients locations often.
