@Joe-Schmitt Well I feel silly. I’d forgotten that I had posted this and had moved on to new things. And I came back around, looking for the solution again and lo and behold, I see that I had posted the question and there was a reply to it.
Anyways, yes, we upgraded from 1.2.0 to 1.3.4. We have the legacy client (from 1.2.0) on most of our systems and if I uninstall and try to install the smartinstaller.exe or the new msi, I get the message saying that I need to uninstall the old version.