Somewhere during the 4.11 betas/rc's, after a plasma crash, I ended up with two of the notifying widgets (they slide in and covers the important places I want to look at ALL THE TIME).

I tried to see if I could get rid of them by editing the rc files, but I can NOT find out where this information is kept.

Do I really have to delete anything related to plasma and start all over establishing my desktop?

Are you able to tell if these notification widgets are attached to a panel in any way, or are they positioned off screen?
In any case, if you are quick enough (and have widgets unlocked) try right clicking on the notifications when they show up and select "Remove Notifications" which should remove these broken applets.