At the moment I'm using the 64-bit install of X1. I have X2 but haven't installed yet until I can get these plugin issues solved.

Re-registering the plugins? I'll have to look into that. Never done it before.

What I'm trying to determine is if the .dll name and/or folder structure is relevant to the problem, or whether it's a deeper parameter, like the CLSID that SONAR uses to ID the plugs. I've always thought this was a shortcoming in DAWs...even though it's probably unavoidable to some extent since the plugins are mostly 3rd party. 

When I rebuilt the DAW, I was foolishly hoping to just install the most recent versions of plugins and keep the system lean. But now I realize I've got to put them all back in, and since I don't recall if I used DXi or VST versions of them it's kind of a nightmare. 

Disclaimer: this is all my own frickin' fault. Before I built the new DAW I could've done a million things to help ameliorate this problem. Image the old DAW, render all my tracks as audio, gone through and manually updated each synth to the most recent version, blah blah. But I've got a whole album on there and since I have the square peg AND the square hole I just want to reconnect them. 

...wicked

Yah did scans. Plugin shows up in my menus and installs and runs fine, just doesn't seem to be recognized in an older project as that plugin.

Are you sure that the missing plugins are not DX rather than VST?  I have several plugs in both types and in old projects it is not always obvious which one I chose when I inserted it.  Nowadays I always chose the VST version.

EDIT: Sorry, I was replying to Post#8, but I now see that you have already addressed this issue in Post#11.