You are absolutely right mharvey
This is what the Solarwinds Support returned:
1. Agree, there are no release notes for Additional Pollers
2. You only have to think about upgrading an Additional Poller, when you upgraded a Solarwinds "Main Poller Module on the Application Server"
3. In the bundle version you can't see which module poller has been updated by Solarwinds
4. You can check on Customer Portal, in the list of seperate Additional Poller downloads below the bundle which version has been updated...
So the process I would recommend:
A new SW Module version is released, you upgrade your main poller and then check on Customer Portal if there is a new Additional Poller Bundle version.
Double check with the individual Poller package list below on Customer Portal and finally update the bundle to gain the Poller Version for your upgraded primary Poller...