Prior to the March update, the PRV featured a tab that allowed the user to see multiple tracks in the PRV.  That tab has gone missing in the March update.  Is that feature gone gone or has it just gone somewhere else and I haven't found it yet?
 
thx
 
//p

In a nutshell, open up PRV and press "h" to bring up the Track pane on the right.  There you will see a list of all tracks in your project (including audio) with the highlighted one being edited.

With auto-lock off, hold shift while pressing another track in the Track pane to make that track visible and editable.

With auto-lock on, tracks that you aren't editing are still visible, but greyed out and uneditable .

I suggest you have a look at the user guide (New Features - Piano Roll enhancements)  that explains the new features of the PRV since the march 2017 update.

I hope that helps.